DM42 RPN Scientific Calculator – Advanced Programmable HP-42S Upgrade for Engineers, Students, and Professionals

The DM42 is a wonderful device. For those who love the Pioneer series of HP calculator, it doesn't get any better than this. . . .and for a price that is less than a decent, used HP-42S.I too had some keyboard issues. Michael at Swiss Micros helped me out. It took some time and some patience (and trust), but the end result is so, so worth it. I would feel confident ordering from them again; however, I don't think I would be confident ordering if I needed something right away. . . . as I said, it took some patience. . . ..but is was so, so, so worth it. I am confident they will be able to get to where less patience is needed (they may have already done so--the one reviewer with a 3737 serial number was higher than mine). If you check out their web site, you will note that they appear to be a small company. This comes with potential for needing to be a little patient (that is so, so worth it), but it also comes with a tremendous level of personal support and connection to a really fascinating community of experienced and dedicated RPN users. In the end, this is quite a good deal.This calculator has all of the functionality of the HP-42S. The fabulous screen lets you see the entire stack and is very easy on the eyes. It's size and feel are absolutely wonderful. Did I mention the screen is fabulous.I bought this for my Daughter instead of the HP Prime or HP-35S. She is going into Engineering next year, and several weeks ago she said, "Dad, I want to learn RPN"--talk about a proud papa moment.The reason I bought this over the HP Prime for my Daughter is that at least some Exams (like the NCEES Fundamentals of Engineering) only allow the HP-35S or 33S for RPN models. Many classes in Engineering schools only allow these or "non-programmable" models, so I wanted her to be comfortable with RPN that had a 4-level limit on the stack (like the 35S and 33S). I learned on an HP-48SX (and as the HP Prime would), this promoted an entry style that is not easily transferred to the 4-level stack limit found on the HP-35S. While still "Reverse Polish", I enter numbers in a different order and never use the Swap or Store functions. . . . as is typical with a 4-level stack on more complex problems.I got this for her over the HP-35S partly because it was a gift for Christmas (and I wanted to do something special). Also, I liked that she could see the whole stack and hopefully get a better feel for what happened with stack overflow (and how to avoid it). It also appears to be far more durable, much smaller. . . . etc. etc. etc.My Daughter was a little frustrated while we got the keyboard issues worked out. Since then, it has turned within a matter of a couple days into her "go to" calculator. She only uses her old TI-84 if she wants to graph something.I haven't decided yet whether or not I will get a DM42 for myself. I always thought I was an RPN user, but I was actually an RPL user. It is not that I have anything against the people who use the 4-level-limited stack--I admire them greatly. I simply don't trust myself with the possibility of unnoticed Stack overflow after using an unlimited stack for 25+ years. I am leaning more to the HP Prime for myself mainly because of the unlimited stack and because the functions that I use most frequently (like those of the HP-45) are immediately accessible on the HP Prime. It's kind of strange that even though I need less functionality than the HP-35S gives, I will likely end up with the HP Prime for the unlimited stack that is most like my 48SX. I am waiting until the HP Prime is available with the G2 hardware in the US. Until then, I am using the HP Prime App at work due to the larger stack that I am more comfortable with. If the DM42 (or derivative of it) has an expanded stack available by then, I will likely buy that over the HP Prime due to the size, feel and build quality.My desire for a larger stack doesn't take away from the DM42. For what it is meant to be and for its target market, it is absolutely magnificent. Even though it took some patience, and it may not be the best for me, I still give it 5+ stars

I have been a calculator fan since the late 70's - back in the days when calculators were instruments, not disposable electronics. When I saw this calculator, I had to have one. In fact, I purchased a few different models. There is no doubt that this is a fantastic product. It's solid and well-made. The display and everything about it is cool. It does a great job of emulating the original calculator, with a few bonus functions.I have not had a keyboard issue (missing key presses) with this specific calculator, but I did purchase the DM16L from the same company. That calculator has keyboard issues. As an Engineer, I think the issue acts like keyboard input is polled - not driven by interrupts (or interrupts are not buffered or serviced fast enough). The DM16L simply loses key presses. The DM42, seems to do much better. I would recommend that the manufacturer concentrate in this area - it's a primary part of the user experience. For the DM16L, it makes the calculator mostly unusable for an every day tool, and relegates it to toy status.I miss the multi-sided keys of the original HP calculators. I'd pay more to get that aesthetic. After all, nostalgia is a main driver for the purchase of this calculator. Why not go all the way?I look forward to future calculators from this company. Some of the older HP's (e.g. HP41C) or even a few TI dinosaurs (SR52/56/59) would be nice.

This is the best calculator I have ever had the pleasure to own and use. Bottom line... it works and works well. In terms of pure calculating, there is very little it cannot do. From simple numbers and calculations to complex numbers, matrix mathematics, advanced functions, and programming to the ability to create and store multiple states of the calculator and maintain and create backups and programming offline from the calculator, this ends up being a very versatile tool with few practical limits.There are a few brilliant touches here that make the calculator much easier to use than its predecessor (the HP 42s, which was/is a very good calculator). Just to point out a few of them... the row of dedicated soft keys at the top of the keyboard reduces the overlap of functions and lets one program a more user friendly interface. The display showing all 4 stack registers at once is easy to read and helps one keep a better visual track of calculations as they progress through the stack. The e-ink display in general is great and is adjustability makes it something that can be easy to read for a wide range of people while consuming minimal power.There are other innovations here, but those are a few which have been most noticeable and practical for me in my day to day use. The keyboard is solid with a good feedback and, in long term use, has become my favorite keyboard among my many calculators. The case and body is solid, mostly metal design using titanium with a back surface that has just enough stiction to remain comfortably firm and set solidly in one’s hands and fingers. It also has just enough heft for one to know they have a positive grip on something.A bit of a plus feature for those who have an HP infrared printer... it will print to it. Though I first thought that would be a novelty, I have ended up using it far more than I would have expected.If you want one last forever calculator, this could very well be it. There other very nice ones that do CAS and make pretty pictures. But for pure number crunching, one would be hard pressed to find a better pocket calculator (that actually fits in your pocket!).