Thomas Denney

Abbey Road

Abbey Road pedestrian crossing
The pedestrian crossing near Abbey Road Studios today

In normal times, tourists would disembark the Jubilee Line at St John’s Wood and walk down Grove End Road to imitate The Beatles’ famous album cover outside Abbey Road Studios.1 On my morning runs I’d usually see a group gathered outside the studios hoping to dodge the traffic for a moment to take their souvenir photo.

Today there was nobody.

As the world enters lockdown we’ll see many more photos of tourist attractions, business centres, and sports stadiums devoid of people. Right now, these photos seem strange: the very absence of people from our shared places makes them feel lonely, spare, and purposeless. Without tourists and Beatles fans, this is just a pedestrian crossing. Without traffic, it barely need serve that purpose.

News organisations should share these photos: they are evidence that people are following guidance to stay home, and that is newsworthy. On Friday evening, after Boris Johnson announced pubs must close, thousands descended on their locals to get in one last pint. It was disheartening to see people wilfully miss the point, but at least we’re now seeing that people can and will listen to government guidance.

However, when we look back at the Covid-19 crisis I don’t think we’ll reflect too hard on photos of empty streets and spaces, precisely because they are empty. This crisis wasn’t caused by people, but people can manage it, and images of what people have done and will do will have far greater lasting impact. Not all of that is good: raiding supermarkets shelves is a selfish and unproductive approach to the coming weeks.2 But in others we will see the very best of humanity, and we should record and celebrate their efforts.

All of this is to say that my photo of Abbey Road is fairly pointless; a momentary capture of an unusually quiet morning in North London.

  1. Last week, I came across a group taking a similar photo at entirely the wrong pedestrian crossing a little further up Abbey Road. I’ve no idea if they’d made a genuine error or had eschewed the crowds outside the studios, but I found it delightful nevertheless.↩︎

  2. Also, toilet paper?! What are you all planning?↩︎

Californian Landscapes

Silver Lake
Silver Lake
Convict Lake
Convict Lake
Ice at the edge of Convict Lake
Ice at the edge of Convict Lake
Trees near Lake Tahoe
Trees near Lake Tahoe
Looking towards Lake Tahoe
Looking towards Lake Tahoe


A Sujiko puzzle. The digits 1-9 are arranged in each cell so that the value in each circle is the sum of the surrounding cells.

Sujiko is a puzzle often featured in British newspapers. The idea is simple: arrange the digits 1-9 in a 3x3 grid, using each digit exactly once, such that each 2x2 square’s sum matches a given value. To start the reader off, one or two of the cells are filled with clues.

My immediate reaction to discovering these puzzles yesterday is that they are ‘boring’, by which I mean trivially solvable by a computer. Secondly, I noted that the state search space for a potential solution is remarkably small compared to other common ‘newspaper puzzles’ like sudoku: there are around 6.67 × 1021 possible sudoku puzzles, but just 9! = 362,880 possible Sujiko puzzles. However, with 2 clues it is only necessary to check 7! = 5,040 possible digit permutations.

But the state search space can be further reduced! Once values for the five non-corner squares we can determine the values we would have to select for the corners (per the sum constraint); the solution is valid if we can select four values for the corners that have not already been used. Assuming two clues are given, this reduces the search space to 7 × 6 × 5 × 4 × 3 = 2,520 permutations in the worst case, but we can still do better!

Wikipedia notes two identities that can further reduce the search space:

In the case of the puzzle at the beginning of the article we only need to select one of 7 possible values for the centre square (x4), which then gives a value for the square to its right (x5). With a centre value selected and the opposite corner already known, we can find the value of the bottom-left corner (x6). From there we only need to fill x7 with one of four remaining digits: this will then constrain all other cells. Therefore there are only 28 permutations to check for the above puzzle — or any other puzzle with clues in the same position (including symmetry).

For any arrangement where the two clues are directly opposite (e.g. in x1 and x7 or x3 and x5) we should firstly fill the centre (x4) with one of 7 possibilities and then another non-corner (e.g. x7) with one of 6 possibilities. From there we can derive all other cells.

For arrangements where the 2 clues are on the same diagonal, It is then only necessary to select one of 6 values for one of the non-corner cells, from there another cell value can be derived, and after that only of four values needs to be selected for another non-corner cell: after this all other cell values can be derived: 24 permutations should be checked in all.

For puzzles with only one clue it is only necessary to place one value (of a possible 8), and preferably to minimise the number of subsequent permutations to check. In the worst case only 8 × 42 = 336 possibilities need to be checked.

From what I’ve seen, puzzles with 2 clues are labelled ‘hard’ whilst puzzles with a single clue are ‘extreme’ in difficulty. Clearly enumerating these by hand would be incredibly dull, but these can be enumerated in well under a micro second on a computer.

Last night I threw together a general purpose solver for these puzzles, and in my experiments it can solve the general case in under 3 μs (alternatively: it could solve every single Sujiko puzzle ever published in a British newspaper in under a thirtieth of a second). The main algorithm is just a recursive backtracking search with constraint propagation.

To accelerate the solver I wound up on a journey into SSE instructions (most of the puzzle state is stored in a single xmm register) at about 3AM, but I’m happy with the results. The solver could be accelerated further with a little more inline assembly to reduce main memory interaction and specialisation for each possible starting layout.

The United States is One of the Oldest Countries in the World


“Hey yo, I’m just like my country, // I’m young, scrappy, and hungry,” begins the song My Shot from the musical Hamilton. The image of the United States as a new, young nation independent from the empires of old is one reflected in both history and the present day: the history books tells us that the US is part of the “New World” that was “discovered” by Europeans in the modern era, and every year Americans celebrate their country’s birthday on the Fourth of July. However, when we consider the radical political change in the rest of the world since 1776 a different narrative emerges.

We begin by adopting and adapting the American definition: a nation began when it most recently adopted a new constitution or a law that declared a new nation, independence, or substantially different government. Ironically, this shifts the establishment of the US to 1787, when the constitution was ratified. Nevertheless, this definition places the US as the fifth oldest nation in the world, after the Vatican (1274), San Marino (1600), Morocco (1631), and Oman (1749).

This definition is far from perfect. The first problem is that nations are often established or re-established in homage to older nations. The modern Republic of France is politically divergent from the Kingdom of France1 yet they still occupy a similar territory, share the same name, and speak (roughly) the same language. Often when nations gain independence they revert to their pre-colonial borders and names, but with forms of government very distinct from colonial or imperial rule. The introduction of a formal constitution isn’t necessarily an indicator of a new nation: many just codify existing norms.

However, it isn’t necessarily wise to ignore governmental changes, because we would might miss the big gradual evolutions: the Roman Empire began in Rome in 27 BC, but the Byzantine Empire, one of its later forms, ended with the Fall of Constantinople in 1453 AD over 1,000km away. States are perhaps the biggest examples of the Ship of Theseus.

If we relax the definition of the establishment to most recent acquisition of independence or sovereignty the results remain similar: the US is the tenth eldest country.2 Even if we switch to first acquisition of sovereignty the US places 57th, which is still in the eldest third of countries.

Countries that first gained sovereignty or independence before the US are highlighted in brown. Former British territories are pink, former French territories are blue, former Spanish territories are yellow, and former Soviet states are red. All other countries gained sovereignty by other means.

The data are unsurprising when we consider events since the 18th century. The United Kingdom comprised separate kingdoms until 1707, and consequently any country that was not recognised as sovereign, but later gained independence from the British Empire later is newer. Plenty more countries formed during France and Spain’s decolonisation. The end of the imperial age affected the age of almost every country in the Southern Hemisphere from the early 19th century onwards. Eurasian sovereignty evolved radically over the 20th century as countries were absorbed into the Soviet Union, yet mutated once more before the close of the century with the bloc’s collapse. Simply put, US longevity depends on an early imperial exit and a distaste for communism.

An alternative definition would be to consider when the colloquial name of a country changes. This is a helpful proxy for countries established before constitutions were en vogue but language evolution is a hindrance: England is not necessarily a distinct country from the (rather charming) Old English Englaland. Languages and nations evolve asynchronously. It would be unreasonable to fix the definition to a particular language; using English would just reflect the international politics of the Anglosphere.

Ultimately, regardless of the path we take, any attempt to unambiguously define how countries are established will see the US in at least in the older half of nations. This is primarily the result of decolonisation in the mid-to-late twentieth century and the later collapse of the Soviet Union: until many countries left these supranational blocs they didn’t necessarily fit our modern definition of a nation. It is perhaps also a testament to the influence of the US’s Constitution (and in turn the Magna Carta, amongst other documents) that the US has fit within the modern definition of a nation for so long, and that so many countries modelled their governments after the US.

  1. Since the late eighteenth century, France has been a kingdom, a republic (1792), an empire (1804), a kingdom (1814), a monarchy (1830), a republic (1848), an empire (1852), a republic (1870), an occupied territory with a republican government in exile (1940), a provisional republic (1944), a republic (1946), and finally a revised republic (1958).↩︎

  2. In order: Portugal (1139), San Marino (1503), Spain (1516), Sweden (1523), Morocco (1631), Bhutan (1634), Liechtenstein (1719), Oman (1743), and Nepal (1768).↩︎

JIT Compilation on an ARM Cortex M0

For my bachelor’s thesis last year I implemented a JIT compiler for the BBC micro:bit, a micro-controller that is being used around the world to teach programming in schools. My compiler took bytecode for a virtual machine designed by my supervisor, compiled it to ARM Thumb bytecode, and executed the generated bytecode. The main challenge here is getting the JIT compiler to store the original virtual machine bytecode, auxiliary data structures, compiled bytecode, and program data in 16 KB of RAM. Rather than replicate my thesis in full here I’m just going to run through the basic steps involved to JIT compile and execute functions on a Cortex M0; I assume familiarity with C++ and ARM Assembly and calling conventions.

At a minimum, a JIT code generators needs to perform three basic steps:

  1. Generate a sequence of instructions encoded in the processor’s bytecode;
  2. Jump to that sequence of instructions, allowing the processor to execute them; and
  3. Return from the generated code to the environment.

The simplest way to get this working is to generate a sequence of instructions terminated by bx lr, which corresponds to a return in ARM assembly, and then to call that sequence of instructions as if it is a function:

typedef void (*f_void)(void);

static const uint16_t instrs[] = { 0x4770 };
f_void fp = (f_void)((unsigned)instrs | 0x1);

In this basic example our generated code is a compile time constant, but this example adapts to dynamically allocated arrays too. 0x4770 is the hexadecimal encoding of bx lr, the ARM instruction that corresponds to branching to the address in the link register, which will be the return address:

Note that the Cortex M0 executes Thumb bytecode, which is a compact version of the full ARM 32-bit instruction set; most instructions are represented in 2 bytes. The most significant 9 bits of this instruction encode that this is a branch and exchange instruction and the subsequent 4 bits encode the register that contains the address to jump to (the link register is register r14). The last three bits should be zero.

Next, two inline assembly instructions are issued. DSB is a data synchronisation barrier, and ensures that no instruction in program executes until after this instruction completes, i.e. the instruction ensures that all memory operations complete. Next, ISB is an instruction synchronisation barrier, and flushes the fetch pipeline of the processor. In this case, where our JIT’d code is actually in a static array, these instructions are not necessary. However, when generating instructions it is necessary to ensure that (a) our generated instructions are fully written to memory, and (b) the fetch pipeline doesn’t attempt to fetch the old value. These instructions must be issued across all ARM architectures (not just the Cortex M0) when running JIT’d code.

Memory protection typically prevents memory being both writeable and executable, so in JITs on other OSes it would generally be necessary to prevent writing and only permit executing the code. No such protection exists on the Cortex M0, so only DSB and ISB must be executed.

Next, we cast the pointer to the instructions sequence to a pointer to a function pointer so we can call the code. Our array will be 2-byte aligned (which is required for Thumb instructions), but when branching the LSB of the address we jump to must be 1 to indicate that the instruction we are jumping to is encoded in Thumb bytecode rather than full 4-byte ARM bytecode.

Supposing we have access to a memory allocator, we can adapt the above to dynamically generate the same function at runtime:

uint16_t* instrs = (uint16_t*)calloc(1, sizeof(uint16_t));

instrs[0] = 0x4770;
f_void fp = (f_void)((unsigned)instrs | 0x1);


This function isn’t particularly interesting: it has no observable side-effects and doesn’t return anything. As a toy example, the following function JIT-compiles a function that sums between 0 and 4 integer values. The first four integer arguments are always passed in registers under ARM calling convention, and the result of an integer function is returned in r0.

typedef int (*f_4_int_to_int)(int, int, int, int);

int jit_int_sum(unsigned int n)
    std::vector<uint16_t> instrs;
    if (n == 0) {
        // MOV   Rd  Value
        // 00100 000 00000000
        // 2   0     0   0
    } else {
        for (unsigned k = 1; k != n; ++k) {
            // Rd := Rn + Rm
            // Add     Rm  Rn  Rd
            // 0001100 000 xxx 000
            // 1   8    0    0
            instrs.push_back(0x1800 | (k << 3));
    instrs.push_back(0x4770); // Return

    auto fp = (f_4_int_to_int)((unsigned) | 0x1);
    return fp(1, 2, 3, 4);

Note that this time I’ve used a C++ vector to simplify the memory management. In this example we either clear the return register or sum up to three remaining registers into the first register. For simplicity, the function pointer is always cast to the same type and called with the same number of arguments, but the return value of the function will differ depending on the value of n.

Encoding instructions manually in hexadecimal (or binary) isn’t a particularly good use of your time. In my project I implemented a library for all Thumb instructions, and eventually I also implemented a decoder to help with debugging. Helpfully the decoder (printFunction) can take a pointer to an arbitrary ARM function, allowing runtime bytecode -> assembly conversion.

The next challenge is dealing with branches. In a traditional compiler this can be delegated to a linker, but in a JIT where all code bytecode must be generated it is necessary to deal with them yourself. The conditional branch is encoded as:

The condition is a 4-bit value and is used in conjunction with the condition flags of the CPU to determine if the branch is taken. I specify the values of these conditions in my instruction encoder here. The immediate value is a signed (two’s complement) 8-bit integer. If the condition holds, the value is sign extended to a 32-bit value, doubled, and added to the current program counter, so that the branch supports offsets from -256 bytes to +254 bytes. However, it is important to note that the program counter, at the time the branch instruction begins, is the address of the branch + 4 bytes. Therefore if the conditional branch needs to skip forward by 2 instructions, then the offset should be 0. If the branch needs to skip back 10 instructions, then the offset should be -12. The same encoding scheme is necessary for unconditional branches and bl/blx instructions (used for functional calls), although these both admit 11-bit offsets.

The examples above are able to freely use registers because they conform to the basics of ARM calling convention; dealing with function calls and access to other registers only requires that you follow this convention in generated code.

The full code of microjit is on GitHub. I’ve also uploaded a barebones example showing the examples from this post executing.

Pilot E95s

Pilot E95s

The Pilot E95s is a pocket fountain pen released by Pilot to celebrate their 95th anniversary. The pen sports a classic mid-century design based on the Pilot Elite, and it makes for a great combination of vintage design with modern manufacturing. I own the ivory and burgundy pen, but it is also comes in black (as all great products should). Both colour schemes feature a large 14K carat gold nib, which has been superb to write with.

Japanese nibs tend to come up narrower than American or European nibs and the Pilot E95s is no exception. I have the medium nib, but it comes up no thicker than fine Lamy nibs, as shown below.

J. Herbin Rouge Opéra, Pilot Iroshizuku Take-Sumi, and De Atramentis
Dunkelblau inks on Tomoe River paper (the nicest paper I've ever written on,
but sadly difficult to get hold of in the UK).
J. Herbin Rouge Opéra, Pilot Iroshizuku Take-Sumi, and De Atramentis Dunkelblau inks on Tomoe River paper (the nicest paper I've ever written on, but sadly difficult to get hold of in the UK).

The pen is compatible with Pilot's CON-20 and CON-40 converters. I'm not certain that there is enough space to use a cartridge. To the pen's detriment the converter is almost entirely covered by the screw thread for the body, making it impossible to see how much ink remains in the converter. The converter itself contains a ball that will rattle when the converter is empty, which can be irritating whilst writing.

The E95s is indisputably a premium fountain pen, and it's an affordable introduction to gold nibs. However, I found that it didn't feel like a premium fountain pen: it feels too lightweight. This is entirely down to resin construction, which makes it a lot lighter than other pens in its price category. At 17g, its weight is comparable to the larger TWSBI Go or Lamy Safari, although each of these are larger. I'm currently using a Lamy 2000 as my primary pen (25g) alongside a Pilot Vanishing Point (30g), so I've found that I notice the E95s's weight every time I write with it. Regardless of its weight, I could replace either of my daily drivers with the E95s if need be: its nib is incredibly smooth and it writes well on a variety of surfaces.

Whilst I researched this review I attempted to find out a little about the history of the pen, but instead I found a myriad of inconsistencies! Firstly, the name of the pen is different in the United States and Japan. In the US it is marketed as E95s (although the case of the “s” varies between suppliers and Pilot's websites), whilst it is called the Elite 95s in Japan. The name also affects the design, with the Japanese version inscribed with “Elite” rather than “E”, as in the American version. I think the “Elite” inscription looks better.

Pilot E95s

Most distributors describe that the E95s is based on the Pilot Elite, which was originally released in either 1962 or 1968. However, neither date is correct! Whilst it is certainly true that the Pilot Elite was sold in the 1960s, and embodies the design of that decade, Pilot Japan's website (Google Translate) states that the first Elite was released in 1954, and that the E95s is actually based on a later second edition released in 1974. This corroborates with the appearance of Elites that I've found on eBay, and this excellent post on the fountain pens subreddit compared the E95s with an older Elite. Noticeably, the nib of the E95s is much larger.

Pilot E95s boxed; the Vanishing Point comes in the same box
Pilot E95s boxed; the Vanishing Point comes in the same box

As well as its history, pricing and availability of the pen is sadly also inconsistent. In Japan, the pen retails for ¥10,000 (around $90 at the time of writing), but in the United States its retails at $170, although The Goulet Pen Company sells it at $136. I definitely prefer both the Lamy 2000 and Pilot Vanishing Point, which are priced similarly, which typically sport rhodium-plated and black-ionized gold nibs.

Older Pilot Elites, in varying conditions, are also available on eBay for prices that dip below $30, so this is a more affordable option. However, as a great modern introduction to gold nibs, the E95s serves nicely.

Oxford through the pinhole

Last summer I bought a Pinhole Pro “lens” for my camera, but I hadn’t experimented with until I went for a walk round central Oxford this morning. The lens I have has an focal length of 58mm, so many of the images below are out of focus. I think it produces an interesting ethereal effect, and achieves a lot of Instagram-esque effects in camera.

I had to touch up each of the following a little; before I set out I didn’t realise that there was a small amount of dirt inside the lens, which meant that all the images were initially marked with the same pattern.

Tourists in Radcliffe Square. Even in bright sunlight (Oxford is seeing
unusually nice weather for February) I had to expose the image for 4 seconds at
ISO 100. Any motion thus appears blurred, so a tripod was a
Tourists in Radcliffe Square. Even in bright sunlight (Oxford is seeing unusually nice weather for February) I had to expose the image for 4 seconds at ISO 100. Any motion thus appears blurred, so a tripod was a necessity.
Looking east on Broad Street. This was a 1 second exposure at ISO 400. Balliol
College, left, has a nice glowing effect, which was achieved entirely in
Looking east on Broad Street. This was a 1 second exposure at ISO 400. Balliol College, left, has a nice glowing effect, which was achieved entirely in camera.
Brasenose Lane from Radcliffe Square. 1 second/ISO 400.
Brasenose Lane from Radcliffe Square. 1 second/ISO 400.
Bridge of Sighs from the Old Bodleian. 0.8 seconds/ISO 400.
Bridge of Sighs from the Old Bodleian. 0.8 seconds/ISO 400.
Sports fields and Merton College from Christ Church Meadow. 0.5 seconds/ISO 400.
Sports fields and Merton College from Christ Church Meadow. 0.5 seconds/ISO 400.
The Cherwell, Christ Church Meadow. 0.5 seconds/ISO 400.
The Cherwell, Christ Church Meadow. 0.5 seconds/ISO 400.
The bridge that joins The Cherwell and The Thames. 2.0 seconds/ISO 100.
The bridge that joins The Cherwell and The Thames. 2.0 seconds/ISO 100.


The TWSBI Go, a new demonstrator pen from the Taiwanese manufacturer, was released in August 2018 and I purchased mine shortly after its release. I’ve been using TWSBI pens on and off for the last couple of years (I wrote all my finals with a Diamond 580 last year), but until this week I hadn’t spent much time with the Go.

The body of the Go is an all plastic construction, and this makes the pen very lightweight. All the plastic is translucent, and the body is available in either sapphire, pictured, or “smoke”. By far the most interesting aspect of the pen is its filling mechanism. Like other TWSBI pens it doesn’t require a converter or cartridges, and instead includes a spring-based vacuum filling system. All my other pens use screw-based systems, so this was a novelty for me. I’m not a fan of this system because I nearly knocked an ink bottle over whilst releasing the spring, so it serves to be careful.

Unlike other TWSBI pens, the cap doesn’t feature a clip. Given that the pen is marketed a pocket pen, I think this is a disadvantage. Instead, TWSBI replaced the clip by a hook for a lanyard. I haven’t seen this on a pen before, but it doesn’t strike me as very useful. The cap is made of plastic, and it is only a little wider than the body. This means that it posts tightly, but I’ve avoiding doing so out of fear that the plastic may crack.

Overall, for the price, the pen writes well and although a little, a comparable experience to the TWSBI Eco. As far as I can tell they both use the same steel nib, although the markings are clearer on the Eco. Both sections are a traditional hourglass shape, but the triangulated shape of Eco is easier to hold.

Left-to-right: The TWSBI Go, Eco, Diamond 580
Left-to-right: The TWSBI Go, Eco, Diamond 580

At $19 it is around $10 cheaper than the Eco, previously their most affordable offering. If you want a great demonstrator I’d recommend getting the Eco over the Go, because you’ll get a slightly bigger pen that rests more comfortably in the hand. Alternatively, if you’d like a pen that your friends will mistake for a vape, the Go is a great choice.

Namisu Nova

Namisu is a company that designs fountain pens in Fife, Scotland. They’ve been operating since 2013, but I only discovered their work earlier this year. As far as I’m aware there are relatively few British pen manufacturers, with most expertise now found in Germany and Japan, so I was keen to try out their work. Predominantly focused on minimalist design, their pens are devoid of any of their own branding. They compensate for this with distinctive shapes and high-quality materials.

The Nova is one of their earliest designs, and has been available for three years. I have the aluminium model in red, although it is also available in brass, titanium, and other colours. Of these, I think the titanium looks the best and I imagine they don’t differ in their ergonomics. Namisu currently also ship the similar Orion and Ixion pens, along with a few rollerballs, although these are more expensive than the Nova.

Each of their pens ships with nibs produced by Peter Bock in Germany. The choice of Bock nibs is a pragmatic one, I think, as they are both a reliable and relatively inexpensive choice. My Nova has a fine steel nib, although titanium and broader nibs are also available. I initially struggled to get ink flowing through the pens, and experimented with a number of inks and notepads, but continued to find that the nib scratched the surface of the paper, often without flow. However, after flexing the nib a little I eventually managed to get ink flowing comfortably from the pen without issue.

The Nova ships in an attractive box and with a standard international converter
The Nova ships in an attractive box and with a standard international converter

Although it looks very nice, I didn’t find the Nova terrificly comfortable to write with, especially for longer periods. The section — the part you grip with your fingers — is wider than any other pen I own, and its surface is completely flat, rather than a gentle curve or moulded grip seen on other pens. Those with small hands may find the pen uncomfortable to maneuver, but I can certainly see the pen being more comfortable for those with larger fingers. The flat surface was a bigger issue, especially considering that the pen seemed to initially require significant pressure to get ink flowing, with my fingers left with pen-shaped indentations after an hour or two of use. The only other significant downside of the design is that it tended to roll a lot on my desk.

The Nova pictured with J. Herbin Bleu Myosotis ink
The Nova pictured with J. Herbin Bleu Myosotis ink

Overall, I wouldn’t recommend the Nova over other pens in its price category — TWSBI certainly make significantly nicer pens for a similar price — but from an aesthetic perspective it is certainly worth it. There are very few pens with all-metal bodies available at that price, and after about six months of ownership I haven’t noticed a single scratch anywhere on the body; this pen is durable. I haven’t yet experimented with posting the pen, but I wouldn’t recommend it as the cap screws on and off. Prior experience suggests that the screw thread is likely to eventually damage the body.

The Nova is available at Namisu’s online store for £45.


Aluminium KOSMOS ink in Night Sky
Aluminium KOSMOS ink in Night Sky

In general I am not a fan of ball point pens, but the magnetic cap design of the KOSMOS pen intrigued me. Rather than pressing a button or removing a cap, the KOSMOS pen by Stilform, a design studio based in Munich, allows you to pull back on the cap, which is then held in place magnetically. It is a simple but effective idea.

Stilform clearly care about design, and the KOSMOS pen is certainly the best designed ballpoint that I’ve used. That design does come at a price; my aluminium model cost €50, but a titanium bodied model is also available at €100. The aluminium models come in five colours, three of which are intentionally similar to Apple’s MacBook lineup.

Aside from the magnetic cap, one of pen’s best features is barely mentioned in Stilform’s marketing: the pen rolls very little. I suspect they’ve weighted the body on one side, but I couldn’t tell where after playing with it for a few minutes. I was a little disappointed to find that it didn’t always roll to show the logo, which is engraved near the top of the pen. I think the engraving could be a little deeper, but the rest of pen’s design seems to call for minimalism.

I struggled to find good lighting to show the logo’s shallow engraving
I struggled to find good lighting to show the logo’s shallow engraving

Before I received the pen I wasn’t sure which part of the pen actually moves when you shift the cap. The cap screws onto the black segment that initially separates the cap from the body, and both of these move when the cap slides — the refill always stays in place. I’d like the cap to screw in a little tighter, although only because I fiddled with it repeatedly this week! When I did unscrew the cap I found that the spring inside it would often come loose and fall out; I think a grove near the end of the cap could solve this problem.

The pen, with the cap covering the refill cartridge
The pen, with the cap covering the refill cartridge

The pen is loud. Not to write with, but with the snap as you shift the cap in and out of place. By way of comparison, it is much louder than closing the lid of my AirPods case and certainly louder than any other retractable pen that I’ve used before.

The included Stilform cartridge let the rest of the pen down. I initially found that I had to apply a lot of pressure — a lot more than I would apply with other ballpoints — to get a consistent stroke. Thankfully the cartridge is a standard (it is the same ISO G2 cartridge that Parker include in their ballpoints), so it can be easily replaced. Otherwise, the pen is a very comfortable weight and I didn’t have any issues writing with it for a few hours.

On the top line I applied extra pressure whilst on the second I allowed the ballpoint to roll across the paper.
On the top line I applied extra pressure whilst on the second I allowed the ballpoint to roll across the paper.

As much as I like the elegant design of the KOSMOS pen, I’ll continue using fountain pens for regular writing. At the moment I’m carrying it in my backpack for situations where I have to write on paper that ink would bleed on.

Later in 2018 Stilform will release the KOSMOS Ink, a fountain pen with a removable magnetic cap. I’ve pre-ordered the pen, and I look forward to seeing their ideas applied to other stationery.