DM-15L Review

[dm319]

This is a brief review of the DM-15L which I got last week.



Cost/shipping

I bought this for one of my children who expressed an
interest in having a 'weird' calculator. They are 10 years
old and will start secondary school in the UK next Autumn
2025. This model was selected based on calculator exam
requirements and the possibility of a two line display.

I bought this from the SM Amazon store for £150. I did this
deliberately to avoid having to figure out customs charges
for the package. It took exactly 14 days which felt like a
long time, but only because of anticipation, and doesn't
compare to the length of time I have deliberated about it.



Appearance

This calculator feels very weighty, maybe the weightiest of
all pocket calculators I have come across, apart from the
DM42. The sand-blasted titanium rear plate has a rough feel
and very industrial look. It is mated pretty perfectly onto
the plastic top plate.

There is a brushed steel face plate which looks good to me,
but there is a very slight asymmetry in its positioning
which will annoy a perfectionist. The key legends are very
clear, especially the yellow, the blue depends on the
lighting.

Overall, the colours are quite earthy, and the weight gives
it a slight bomb-proof feel. In fact it wouldn't look too
out of place next to world war 2 field equipment in terms of
colours. The hand-stiched leather pouch fits it perfectly
(maybe too tightly but that will improve with time) and
looks terrific.



Keys

The keys are well-formed. Others have mentioned the key
presses are short travel, but it doesn't 'feel' short. If
you are used to HP-65, it will feel short, if you are used
to a Casio or Sharp scientific this has more travel.

It is very tactile and the 'click' is muted. I switched it
to 48Mhz mode fairly quickly which is meant to be better for
key presses and calculates quicker. The most important
thing for me is reliability of key presses, and it does very
well here.

Unfortunately I don't have a good collection of high-quality
HP calculators to compare it against, but my second hand
HP-12c platinum is especially bad in this regard. My rogue
HP-12c is much better than the 12c platinum, but not quite
as good as this. My DM42 is the king of reliable key presses
and is a bit better.

Compared to modern and old Sharps, Casios and Texas
Instruments, this is better than any of them. By which I
mean that often these other brands have a very flat feel to
them, with very little tactility or travel.

There is a very slight discrepancy between the tactile bump
and the registration of the key press. This is familiar and
expected to me given to my experience in mechanical clicky
keyboards. It's normally not a problem as long as you
develop a feel for how hard you are pressing the keys.

Overall, I find the feel of the keys to be excellent.

Display

Is clear to me and similar to the best LCD screens out
there. The DM42 with its high contrast memory display is
better of course. The fonts frankly look terrible on the
stock photos, but it looks good in real life. I don't know
why this is. It is imminently usable and clear.

Functionality

As this was bought to be used in secondary school in the UK,
this is the perspective I'm looking at this from.

Firstly, it is RPN. That's a given in this forum of course,
but the competition for this calculator mainly comes in the
form of a Casio, Sharp or TI scientific non-graphing. I
really wanted an RPN calculator for my kid to learn on as I
genuinely think it is better for 'calculating' than
algebraic. At the moment, for less than 1/10th the cost, I
can get a Casio with a natural layout and which can
calculate to greater accuracy.

On the other hand with the algebraics you can end up at the
mercy of wherever arguments are ongoing regarding order of
operations, which is something you decide for yourself with
RPN. Casio have opted for 'multiplication by juxtaposition'
(a silly term for this IMO) as needing clarification with
brackets. At the same time they are now treating scientific
notation as not receiving any special precedence which means
that 1÷5e2 is evaluated as 20 rather than 1/500th.

Without this turning into an anti-algebraic rant, there are
also issues that changing the format of the answer results
in a re-calculation, which can be very confusing if you have
chained a calculation using 'ANS' from previously and
require it in a different format.



RPN avoids all these pitfalls, but requires that you
understand what you are doing fully, but really, if you are
getting this calculator for school, it is because you have
prioritised RPN over almost everything else.

Despite being based on 43 year old technology, the DM-15L
beats every other modern scientific calculator in complex
number handling. The modern TI-30X pro mathprint and TI-36X
pro which I believe are top of the range scientifics can not
raise complex numbers to anything other than 1, 2 and 3.

It seems to also have the largest matrix handling of any
modern scientifics with up to 8x8 matrices. I'm impressed
that the factorial works continuously and on negative numbers
presumably using the gamma function.

There is no fraction support. Statistics are limited to
sum, mean, standard deviation and linear regression. This
might be an issue in later A-level maths when calculators
may be expected to calculate probability distributions and
medians.

It does have a numerical solver and integrator, which
matches it with the top-of-the-range scientifics from the
major brands. It is programmable, though this will be of
little use for school as programs will need to be cleared
pre exams.

It will not attempt to show results as radicals or fractions
of Pi as many Casios will do these days. On the other hand,
even though this isn't a full CAS system, I think this is
half-way cheating, and it also results in errors when the
calculator gets it wrong.

This isn't the only modern RPN calculator you can buy.
There is also the HP-15CE which is the official modern
re-incarnation of this device. This is very slightly less
expensive here in the UK, but stock is running out rapidly.
It is effectively the same calculator on different hardware,
using a classic 7-segment display and angled HP buttons.

I didn't consider the DM-42 or DM-32 as these are
significantly more expensive and may run foul of rules
around exam use.


Overall Thoughts

This is a very tidy and capable package and, in some ways,
the ideal calculating machine. I am unsure whether this
will work out for my sons education, and I'm documenting the
experience here. The device is incredibly powerful in
some specific areas, more so than any modern scientific
calculator, which is a testament to the effort which went
into its original design. In other ways it doesn't have
functionality which some might expect of even cheap modern
scientifics - fractions, radical and pi representations,
advanced spreadsheets, tables, formulas and statistical
calculations.

However, I don't think these things necessarily help
students to learn, if anything, it might be detrimental, and
learning the principals of maths is more important. To this
end, hopefully the DM-15L will be good, but we will have to
see.

[AnnoyedOne]

(11-09-2024 04:41 PM)dm319 Wrote:  This might be an issue in later A-level maths when calculators may be expected to calculate probability distributions...

FYI the HP-15C Advanced Functions Handbook (AFH) has a program that will calculate the

Normal Distribution Function
Complementary Distribution Function

which should help. Both use the HP-15C numerical integratation function.

A1

PS: I have a PDF scan of the AFH from August 1982, the LE version PDF and the CE PDF. The page numbers of the program above vary.

[Jase]

Great post!
Loved the thoughtful commentary and the pro-level photographs!
Hope the kids enjoy math and do well.
Jase.

[AnnoyedOne]

(11-09-2024 04:41 PM)dm319 Wrote:  Keys

...It is very tactile and the 'click' is muted.

BTW the DM15L has a 4kHz piezo (buzzer) which can be used to provide an audible key press function. I believe that the serial console BEEP command is used to control this.

The unit also has a RTC (real-time clock) chip, NXP PCF8563, which has an alarm function but I don't think that the current firmware supports it.

The documentation re: this is pretty poor IMO.

A1

[Thomas Klemm]

(11-09-2024 04:41 PM)dm319 Wrote:  I bought this for one of my children who expressed an
interest in having a 'weird' calculator. They are 10 years
old and will start secondary school in the UK next Autumn
2025.

I might ask you in a couple of years how that turned out:

(10-26-2024 03:16 PM)Divasson Wrote:  The Spanish school system is strongly biased to Casio units, so giving them a "RPN only" calculator was in a way setting them up for failure.

[Maximilian Hohmann]

Hello!

(11-09-2024 06:51 PM)Thomas Klemm Wrote:  I might ask you in a couple of years how that turned out:

This will turn out exactly the same way as it turned out for me: At some point you will get a letter from the school inviting you to join a discounted collective order for a Ti Nspire (*) because from now on the math/physics/chemsitry teachers will distribute their exercises and homeworks in a form supported only by that platform. To the children that means nothing at all because what they really want is their own smartphone. And a computer with a fast graphics card on which they can play ego-shooter games. Why should your children be different from mine ;-)

Regards
Max

(*) At the school where my wife teaches it is the iPad that was chosen. Children from low-income households will get theirs from the school at no cost.

[Johnh]

Thats a really great review of this machine, from a great Dad!

I have just one thing that Id be watching out for: This is a valuable and unusual machine, potentially a great learning tool. But i would watch out that this doesn't make him feel singled out as being 'different' to all the other kids who are using their Casios in class and throwing them across the playground at recess. My kids are grown up, but if it was me, Id suggest to keep it at home to work on with you, wait to see what the school recommendations are for school calculators and get him whichever of those seems best for use in class.

[dm319]

(11-09-2024 05:03 PM)AnnoyedOne Wrote:  FYI the HP-15C Advanced Functions Handbook (AFH) has a program that will calculate the

Normal Distribution Function
Complementary Distribution Function

which should help. Both use the HP-15C numerical integratation function.

Yes, though the problem is calculators need cleared before exams to meet the UK requirement that nothing is stored on it that can be accessed during the exam. We'll have to see, maybe I'll need to get hold of some GCSE and A-Level maths papers and see if the DM-15L has the features for them!

(11-09-2024 05:40 PM)Jase Wrote:  Great post!
Loved the thoughtful commentary and the pro-level photographs!
Hope the kids enjoy math and do well.
Jase.

Thank you! I hope so too.

(11-09-2024 06:21 PM)AnnoyedOne Wrote:  BTW the DM15L has a 4kHz piezo (buzzer) which can be used to provide an audible key press function. I believe that the serial console BEEP command is used to control this.

The unit also has a RTC (real-time clock) chip, NXP PCF8563, which has an alarm function but I don't think that the current firmware supports it.

The documentation re: this is pretty poor IMO.

You're reminding me of those really old keyboards that used to fire, was it a lump of magnet or metal? whenever a key was pressed by switching on a solenoid. I have a keyboard with Kailh box white switches which are very loud and clicky. It may have been a bad choice. When I'm on a Teams call muted and typing notes, a warning comes up reminding me that my microphone is muted!

I use the date function on my DM42 all the time for calculating all sorts of things, would be nice if DM15L could access that.

(11-09-2024 06:51 PM)Thomas Klemm Wrote:  I might ask you in a couple of years how that turned out:

Yes, please do! Although I don't think this forum notifies you of replies, which means I've often missed replies because I didn't revisit the thread. I'll keep that other thread updated. It may be a short thread.

(11-09-2024 07:25 PM)Maximilian Hohmann Wrote:  This will turn out exactly the same way as it turned out for me: At some point you will get a letter from the school inviting you to join a discounted collective order for a Ti Nspire (*) because from now on the math/physics/chemsitry teachers will distribute their exercises and homeworks in a form supported only by that platform.

This would upset me the most! When I went through school in the UK, they didn't specify brands, and certainly ipads and phones are not allowed in exams, so they will need a calculator of some sort.

(11-09-2024 10:21 PM)Johnh Wrote:  Thats a really great review of this machine, from a great Dad!

I have just one thing that Id be watching out for: This is a valuable and unusual machine, potentially a great learning tool. But i would watch out that this doesn't make him feel singled out as being 'different' to all the other kids who are using their Casios in class and throwing them across the playground at recess. My kids are grown up, but if it was me, Id suggest to keep it at home to work on with you, wait to see what the school recommendations are for school calculators and get him whichever of those seems best for use in class.

Thanks John! I know already what the school recommendation is - the Casio-fx-85GT CW, or the 991 for later years (or if the kids want to show off). My eldest already started at a similar school, and he instantly wanted the school recommendeded. He hasn't minded at all that his younger brother has a fancy/weird RPN calculator and has never said 'please buy me a weird calculator, dad'. My other kid knows it's different and expensive, so I trust him to look after it, but I think he'll need to use it school if he's going to use it at all. But you're right, this could be a short trial!

[Thomas Klemm]

(11-10-2024 11:01 AM)dm319 Wrote:  Although I don't think this forum notifies you of replies, which means I've often missed replies because I didn't revisit the thread.

You can use: Subscribe to this thread
It is a link at the bottom of the page.

[jthole]

I went to secondary school (we have a slightly different system from the UK and other countries) in the late 1970s, children were supposed to know, or learn, how their calculator worked. There was no mandate from the school on which calculator to buy, as long as it was a scientific one, and no real help from the teachers.

Of course modern calculators have a lot more functionality than the scientific calculators of the late seventies, but I would guess that children interested in math and physics, and eager to learn, should still be capable to figure out how their calculator works.

(My children both inherited the interests and talents of my wife, so they went the cultural / languages route instead of math and physics).

[AnnoyedOne]

(11-10-2024 11:01 AM)dm319 Wrote:  Yes, though the problem is calculators need cleared before exams to meet the UK requirement that nothing is stored on it that can be accessed during the exam.

How do they know? I'm sure they know how to check Casio's and TI's but a HP/SwissMicros?

My guess is that anything "not approved" is simply prohibited.

(11-09-2024 06:21 PM)AnnoyedOne Wrote:  I believe that the serial console BEEP command is used to control this.

My mistake. No such command. I don't know what the piezo is there for. No key press audible. No clock alarm so what?

A1

[Maximilian Hohmann]

Hello!

(11-10-2024 01:41 PM)AnnoyedOne Wrote:  How do they know? I'm sure they know how to check Casio's and TI's but a HP/SwissMicros?

In my experience maths and physics teachers are not complete idiots. Questions about which calculator can be used during an exam and how this is to be done are not asked on the day of the exam. This gives the teacher enough time to familiarise himself with the various models.

When I went to school in the 1970ies, there were no clear rules about calculator usage yet. Everyone could bring what he, or his parents, were able to afford. Teachers were smart enough not to look for numerical results in their exams, but for a correct solution. Thereby a better calculator would only make a tiny difference over a simple one - or no calculator at all.

Regards
Max

[AnnoyedOne]

(11-10-2024 02:43 PM)Maximilian Hohmann Wrote:  Teachers were smart enough not to look for numerical results in their exams, but for a correct solution. Thereby a better calculator would only make a tiny difference over a simple one - or no calculator at all.

The same in my day. In fact I don't recall anyone using ANY calculator in a HS math/physics/chemistry exam.

Even in University engineering, although calculators were allowed, it was similar.

A1

[AnnoyedOne]

(11-10-2024 11:42 AM)jthole Wrote:  Of course modern calculators have a lot more functionality than the scientific calculators of the late seventies...

Yeah. I just took a look at the Casio FX-991EX. I think that thing is harder to navigate than a plane cockpit!

A1

[n1msr]

Very interesting post. I will try to follow the progress you post.

I was encouraged to study further maths at A Level in the UK simply because I wanted to know more about hyperbolic functions that appeared on my Texas SR-50A calculator. I was the only one at school with programmable calculators and of course once it was known that there was no equals key, the calculator was safe ;-). I had an HP-67, although I had a TI-57 before that, until an avuncular neighbour showed me his HP-25C and RPN.

10 years old is very young to be using the 15L but thats no bad thing. Maybe you will need to buy a calculator later on that meets the school requirements, but even knowing that there are other ways of doing things (the DM15L) is a good lesson.

Best of luck and kudos to your kid who is prepared to give it a go!

[Commie]

Hi,

The thread starter makes the comparison between the DM-15L and the likes of Casio, TI calculators, I think this is unfair because the TI and Casio calcs cost about £25~£30 whilst the DM-15L costs about £150+.

Also, the TI/Casio use a very easy to use Math Print entry scheme.

I do have a HP15CE and I rarely use it, mainly because it suffers from keyboard bounce and matrix entry is complicated and tricky. In contrast, the TI/Casio matrix entry is a breeze.

The Problem with the HP calculators, is that they are old designs, they were all good 40/50 years ago.

[carey]

(11-10-2024 09:52 PM)Commie Wrote:  The Problem with the HP calculators, is that they are old designs, they were all good 40/50 years ago.

"I find your lack of faith disturbing" -- Darth Vader :)

I agree about inconvenient matrix use for the 15C and its variants. However, for users who value the 15C feature that, except for statistical and matrix functions, all its functions accept complex arguments; that it can do contour integration; and that its integration algorithm is accurate over a wide range of functions (more important than precision for integration as in this recent example), the 40 year old design of this shirt pocket calculator holds up quite well!

[Steve Simpkin]

(11-10-2024 04:32 PM)AnnoyedOne Wrote:  

(11-10-2024 11:42 AM)jthole Wrote:  Of course modern calculators have a lot more functionality than the scientific calculators of the late seventies...

Yeah. I just took a look at the Casio FX-991EX. I think that thing is harder to navigate than a plane cockpit!

A1

Hey, how hard could it be. The Casio fx-991EX User's Guide only has 46 pages. That's smaller than they typical HP calculator quick start guide. And the fx-991EX has 12 different environment Modes to choose from, one for every occasion
https://www.casio.com/content/dam/casio/...1EX_EN.pdf

[dm319]

(11-10-2024 11:42 AM)jthole Wrote:  I went to secondary school (we have a slightly different system from the UK and other countries) in the late 1970s, children were supposed to know, or learn, how their calculator worked. There was no mandate from the school on which calculator to buy, as long as it was a scientific one, and no real help from the teachers.

Yes it seems like that was the way before my time in school (90s). These days with CAS and cheating being a thing, they have to be more prescriptive. At university you needed your calculator approved with a sticker in the run-up to the exams.

(11-10-2024 01:41 PM)AnnoyedOne Wrote:  How do they know? I'm sure they know how to check Casio's and TI's but a HP/SwissMicros?

My guess is that anything "not approved" is simply prohibited.

There isn't really a 'not approved' or 'approved' list, and it seems the guidance is written very carefully. It clearly bans CAS algebra and algebraic solvers/integrators. Strangely it doesn't explicitly ban programmables, instead it says that some types of data must not be retrievable during the exam. This includes formulas, which covers programming. We will have to see whether the 15L is allowed in exams - I have a hunch our school will say no, but bear in mind many scientific calculators can store expressions (including my old Sharp that I used in the late 90s) and these are not disallowed. My presumption is that data is cleared before the exam in order to make it 'fit' for the exam. Another option is 'exam mode'.

(11-10-2024 04:32 PM)AnnoyedOne Wrote:  

(11-10-2024 11:42 AM)jthole Wrote:  Of course modern calculators have a lot more functionality than the scientific calculators of the late seventies...

Yeah. I just took a look at the Casio FX-991EX. I think that thing is harder to navigate than a plane cockpit!

A1

Playing around with the fx-85GT-CW last night I had to go into a menu/submenu to get to %.

(11-10-2024 04:55 PM)n1msr Wrote:  Maybe you will need to buy a calculator later on that meets the school requirements, but even knowing that there are other ways of doing things (the DM15L) is a good lesson.

Exactly!

(11-10-2024 09:52 PM)Commie Wrote:  The thread starter makes the comparison between the DM-15L and the likes of Casio, TI calculators, I think this is unfair because the TI and Casio calcs cost about £25~£30 whilst the DM-15L costs about £150+.

Absolutely accept that cost difference is immense, but a modern scientific is literally the competition if you are a child at school.

(11-10-2024 09:52 PM)Commie Wrote:  The Problem with the HP calculators, is that they are old designs, they were all good 40/50 years ago.

Old doesn't equate to worse. There is plenty of progress which are steps back. Personally I find the HP-42s hit the peak of what I think of as a calculator. This is mainly because of the straight forward RPN entry, and its extensibility with programs that can be written in a way that doesn't require looking up a reference. There's still ways the HP-42s can be improved, but the history of calculators took a different path.

When I recently went on a little adventure testing TVM solvers, the superiority of RPN meshed with a solver became very clear. Most algebraic calculators use a TVM 'app' or table, which is terrible for chained calculations. The voyager HP-12c (and 17bii) was the peak of TVM solving UI, and it actually went downhill with the Saturn graphics and Prime when they followed other makes and made use of a table.

D

[Commie]

(11-10-2024 11:57 PM)carey Wrote:  ...the 40 year old design of this shirt pocket calculator holds up quite well!

If electronics, mainly cpu's and memory capacity, had stood still without the evolution of electronics then I would say you have a good point, however, 40 years of evolution means that hp calculators are somewhat dated now.

HP did ride the evolution wave but only up until hp was broken up into hp/agilent and Keysight.

Cheers
Darren