Staedtler’s new 925 15 mechanical pencil


Today: a quick look at Staedtler’s new 925 15 mechanical pencil. Another pencil I got to know from Gunther.

The 925 15 came out in November 2017, has an official price of ¥500 (~$4.40; £3.30; €3.75) and is available in 0.3mm, 0.5mm, 0.7mm and 0.9mm.

In my opinion, it looks absolutely stunning. The grip section is made from Elastomer. One thing to note: as it is rather rubbery little bits of fibre or dust will easily stick to the grip section.

The push button looks quite different to the push button found on other members of Staedtler’s 925 family. By the way, I have no idea how the numbers after 925, in this case, 15, are assigned. They don’t seem to be in chronological order, but they also don’t seem to indicate how cheap or expensive the pen is. The 925 15 has a much smaller push button than its relatives and comes with a hole. I couldn’t think of any practical use for the hole (checking whether the eraser is used up?) – the only reason I could think of was the same reason why pen caps have holes, so that air can flow in case anyone (most likely children) swallow the cap and it is stuck in the windpipe. ジムキング confirmed that this is the most likely reason for the hole in the push button.

Here’s a family photo with some other 925s.

Top to bottom: 900 25, 925 15, 925 25, 925 35, 925 65, 925 85

The 925 15 is so nice, it deserves a centrefold picture. If it was a bit heavier and had a sliding sleeve it would probably become my daily mechanical pencil.

Challenges 3

Recently, I had the pleasure of talking to Sabine Syfuss-Arnaud, a journalist from the leading French business magazine Challenges. She was writing an article about Faber-Castell and its new CEO Daniel Rogger.

We talked about his plans for China and the factories in Germany, Brazil and China. You might have guessed that I had to mention Staedtler in that conversation (of course) before we talked about what makes the best pencils and other topics.

Challenges N°545 – 7 Décembre 2017

Her article is out now (Challenges N°545 – 7 Décembre 2017).

16.2 13

I’m still not up to date in the world of stationery, so please excuse if this blog post does not include all information, but when I noticed the name Ada Lovelace in the latest Pen Addict Podcast Show Notes I had to have a look.

As you might now CalCedar is releasing themed Blackwings at regular intervals. They tend to have a number linked to the theme. This time the theme is “Ada Lovelace”, considered by many to be the first computer programmer1, and the number is 16.2.

Ada Lovelace, Charles Babbage and Eberhard Faber’s Blackwing

My first university degree was in Computer Science, so this theme certainly made me curious and I followed the link to Blackwing’s web site.

So what does 16.2 stand for? According to CalCedar

The number 16.2 is a nod to the Analytical Engine’s storage capacity of 16.2 kB (0.00005% the storage of the average smartphone) and the backside of each pencil bears a binary pattern stamp of Ada’s initials AAL, the same initials she used to sign her work.

My first thought: if anything this seems more of a number for a Charles Babbage themed pencil. Storage capacity is hardware, Babbage thought of the Analytical Engine, Ada Lovelace was more about algorithms for the Analytical Engine (she made a famous translation of Menabrea’s Analytical Engine article that contained her computer program as notes) and about promoting the Engine.

My second thought: why use kB? I am not an expert in the Analytical Engine, but it was based on the decimal number system, it wasn’t binary based! The only way such a conversion would make sense would be if you wanted to compare the storage capacity to a modern machine, but it only makes sense if you want to implement the same storage capacity on a modern computer, as a simple comparison it doesn’t work because it’s not a simple as some other conversions, like converting Fahrenheit to Celsius – because of the way modern computers work there’s no 1:1 comparison.

Here’s an example. A number with one digit can be anything from 0 to 9, i.e. there are 10 possibilities. If you want to store this number in a modern, binary computer you have to use four bits. Each bit gives you two possibilities (0 or 1). If you have two bits you have four possible numbers (22 = 4) you can represent (00,01,10,11). Three bits give you eight possibilities (23 = 8), i.e. everything from 000 to 111. Four bits give you 16 possibilities (24 = 16). You want to represent one decimal digit (ten possibilities) in binary you need four bits, but you also get some waste (as you could actually represent 16 numbers). So why convert to binary?

My third thought: Where did this number come from. Ah, ok. Wikipedia says in the Analytical engine “There was to be a store (that is, a memory) capable of holding 1,000 numbers of 40 decimal digits each (ca. 16.2 kB)”2.

OK, I get it. The number is from Wikipedia.

A quick check:

40 digits each, 1041 = 2x, 2133 = 1.08 * 1040, 133 bits per 40 digit number

133*1000= 133,000 Bits, 133,000 / 8 = 16,628 Bytes, /1024 = 16.24 kB.

…but the Analytical Engine was an idea, not something that was actually built at the time. Babbage himself wrote

“In the drawings I have prepared I proposed to have a thousand variables, upon each of which any number not having more than fifty figures can be placed.”3

Based on 50 digit figures, as described by Babbage in his 1864 book, the number on this pencil should be

1051 = 2x, 2167 = 1.87 * 1050, 167 bits per 50 digit number

167*1000= 167,000 Bits, 167,000 / 8 = 20,875 Bytes, /1024 = 20.39 kB.

To me, it looks like a poor Wikipedia copy and paste job, done without love or understanding of Ada Lovelace.

My imagination might be running wild here, but I imagine it like this.

We need a new person-themed Blackwing. Pick a pioneer who is not a white male.

I found one on the Internet. There’s a woman who was a programmer.

Great, look at her Wikipedia page and pick a number.

Got it.

Great job. Let’s finish early and go home.

The whole theme seems to have been put together without the due care and attention Ada Lovelace deserves.


Before I finish: there’s actually a quote from Ada Lovelace where she mentions pencils. You can see it on Google Books.

The comic book you can see in the picture is called The Thrilling Adventures of Lovelace and Babbage: The (Mostly) True Story of the First Computer. The edition I got is long sod out but you can still get the US version (hardcover released in 2015) or paperback ..or the UK paperback edition from 2016.

If you would like to learn more about Ada Lovelace have a look at

Untangling the Tale of Ada Lovelace

Ada Lovelace’s translation of the Menabrea article. 

  1. even though computers didn’t exist yet []
  2. []
  3. Chapter VIII, Passages from the Life of a Philosopher, by Charles Babbage, 1864 []

Stationery Factlets: Staedtler Noris digital

Welcome to the first post in a new series on this blog: Stationery Factlets1. This new series was actually born out of necessity. You might remember my current lack of time. To enable me to post with minimal effort I thought of adding this series where I present small bits of information. Many readers will know some or most of these factlets, but you might be surprised by the occasional fact that is new to you or you might be reminded of old bits of information you have started forgetting.

An early picture of the Noris Digital with the Samsung logo. New versions don’t have it anymore.  (Image © Staedtler)

OK, here’s the first factlet.

Staedtler’s Noris digital, their digital pen for Samsung tablets, works with many EMR (electromagnetic resonance) devices (EMR is one of several technologies that makes digital pens work), so it can actually also be used with many WACOM pen tablets (…but because of Staedtler’s current cooperation with Samsung Staedtler’s marketing material only makes reference to Samsung devices).

The images in this blog post have been taken from Staedtler web sites. I believe that the use of the images shown in this blog post falls under “fair dealing” as described by the UK Copyright service.

I would like to thank Benedikt Schindler for the information about the Noris digital presented in this blog post.


Noris digital (Image © Staedtler)

  1. The term factoid has two meaning, so I decided to go with factlet, even though the term factoid is more common. []

Bleistift HQ’s failed attempt to improve paper testing 4

Earlier this year I tried to reduce the human element that is part of my pen and paper tests, e.g. those tests with violin plots. The aim was to make these tests more accurate and reproducible. Plotters are expensive, so I thought I try the :Move mini, an add-on for the micro:bit.

The micro:bit is a small ‘computer’, half the size of a credit card and is used in computer education in the UK. The :Move mini is a robot with two wheels that can be controlled by the micro:bit and that comes with a pen holder.

When I programmed the :Move mini I found it quite difficult to get it to draw a straight line and to have the same reproducible movements on paper, so I contacted the manufacturer Kitronik. Michael Lockhart, who works for their customer service got back to me and asked me to send my :MOVE mini in.

You might have seen this video on my YouTube Channel a few months go.

He told me that they

performed tests at a range of speeds, running at full speed the buggy runs straight and doesn’t suffer with one wheel turning at a different rate. You can reduce the speed to slow the buggy, however the more you slow the speed the more likely the buggy is going to drift to one side. Unfortunately this isn’t a fault with the buggy and more with the way the micro:bit is coded.

By using PWM you define how long you want the pulse to be and the gap between this pulse, as the micro:bit isn’t real time, this causes a slight differences in what the two pins are being told, and this always remains with the same pin. As such this results in one of the pins receiving a slightly different pulse to the other and as such at slow speeds there will be a drift. We had this set to pin 1 at 80 and pin 2 at 100, this is obviously just above/below the stop position for a 360 degree servo.

The longer the pulse is made the smaller the issues with the micro:bit is made, as such you may be able to counter out the issue with the micro:bit by setting the servo’s to half speed[…].

The bad news is that I can’t drive slowly or things go wrong, but if I drive fast things go wrong, too – see the video. Maybe if I could get rubber wheels for the :MOVE mini things would work better with higher speeds.

I also had a question regarding reproducibility as I was wondering whether the charge level of the battery will make a difference. Michael told me that..

In short yes that battery voltage would affect the servos, however it is a little more complex than that. So it works like this:
The servo board has a 3.3V regulator on it which then means the servos are provided with a constant voltage from the 4.5V battery pack. This means that the speed of the servos can be more accurate as when you use PWM you are varying the amount of voltage the servo’s are receiving for a given time. So while the combined voltage of the 3 batteries is between 3.3 and 4.5V the servos will run and you shouldn’t notice any change in there operation.

However once it drops below 3.3V’s the regulator will just pass the battery voltage straight through, this means that whatever the voltage is it will be passed to the micro:bit/Servos. This then means that the voltage that the servos will be provided with can alter and won’t be a regulated voltage. As such this could result in them operating slightly differently, this would normally affect the speed of the servos.

Well, it was interesting to find all these things out, but I am still not any closer to a reproducible pen and paper tester (with the use of a plotter, they cost £200 or more). I noticed that there are R2D2 toys that can draw lines. They are slightly cheaper than a plotter but still expensive.

I guess it might take another few years before I find a good solution…