What a delightful old calculator! Many, many thanks to Niels Wittje from Germany who, instead of turning this poor old machine into useless e-waste or putting it up on eBay in the hope of getting rich on the proceeds, donated it to our site.

At first, I thought I was confronted with an entirely unique beast, but that is not the case. Though its appearance is different, this calculator is really identical to the National Semiconductor NS-4515 Mathematician. Or at the very least, almost identical. It has one odd behavior that is almost certainly a design error, not some unique failure mode specifically affecting this particular specimen: When it displays numbers between 0.1 and 1, it puts the decimal point in the wrong place. That is, instead of 0.5 or even .5, it displays 5 for the value of one half. That's just weird. I do not recall similar behavior from my NS-4515 though it's been a while since I last held that machine in my hands, so I'll have to take a closer look one of these days.

This particular machine also appears... much loved? It seems that several of its keys have been customized. There are also some near-professional quality labels above and below the display that are not factory originals; similarly, some custom labels are also present on the back of the calculator. Given the quality of the labeling and their obvious utility, I decided to keep the calculator "as is" rather than attempting to restore it to a more "factory original" appearance.

Beyond these customizations and the weird display bug, however, it really is the NS-4515 throughout. In particular, the program for the log Gamma function that I wrote for the NS-4515 works on the 600PM without alteration. Just like on the NS-4515, it is fairly accurate for arguments greater than 1: For instance, 5 start yields 24.00004 after exponentiation, which is pretty darn close to the correct result, 24.

MS
EN
ln
×
MR
-
2
π 
×
MR
÷
ln
2
÷
+
1
2
1/x
MR
÷
+
4
0
0
1/x
MR
÷
MR
÷
MR
÷
-