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**Primitive RPN Calculators**

*Posted by Palmer O. Hanson, Jr. on 21 Apr 2004, 12:34 a.m.*

When one thinks of calculators which use the RPN system one usually thinks of the Hewlett-Packard product line. National Semiconductor Corporation (NSC) also made a number of calculators using the RPN system. Two of the NSC RPN devices, the NSC Model 600 and the Novus 650 Mathbox, are easily the most primitive electronic calculators in my collection. NSC made more versatile RPN calculators as well. Two that are in my collection are the NOVUS 4510 Mathematician and the NS4615 Programmable. Other RPN calculators from NSC include the NS 900, the 4515 Mathematician PR and the NS 4525 Scientist.

The NSC Model 600 and Novus 650 Mathbox are four function calculators which implement RPN. The devices have only 15 keys: ten keys for numbers 0 through 9, four keys for the four functions and a clear key. There is no ENTER key. The Enter function and + function are combined on a single key. The devices do not have a decimal point key because they only operate with integers. If the user divides 2 by 7 the machine returns zero in the display. The instruction booklet explains that if you want to see fractional parts you must add trailing zeroes to the numerator and select the position of the decimal point for yourself. That is very similar to the situation we encountered with slide rules in the days before the advent of hand-held electronic calculators. Both devices display a decimal point between the second and third digits from the right as an aid to those who add and subtract dollars and cents but the decimal point has no effect on the numerical display. Calculators can't get much more primitive than that.

The NOVUS 4510 Mathematician which came on the market in 1975 offers many of the capabilities of the HP-35. The exceptions were:

The Mathematician has a second function key (F) which allows it to offer several capabilities not available with the HP-35 including:

The (M + x^{2}) function does not change the contents of the X register but squares the contents of the x register and adds the result to the memory. This feature permits efficient accumulation of the sums needed for single variable statistical analysis. To do so simply clear the stack and the memory, enter each x value in order and press F (M + x^{2}) + for each entry. The sequence ends with sum x in the display and sum x^{2} in the memory, When the data entry is complete press ENT ENT, enter the number of entries, press / and see the mean in the display. Press x CHS MR +, enter the number of entries -1, press / and SQRT and see the standard deviation in the display.

Let's try to do that with the HP-35. To accumulate the sums clear the stack and the memory, then enter each x value in order and press ENTER ENTER x RCL + STO Rdown + for each entry. The sequence ends with sum x in the display and sum x^{2} in the memory. When the data entry is complete press ENTER ENTER , enter the number of entries, press / and see the mean in the display. Press x CHS RCL + , enter the number of entries -1, press / and SQRT and see the standard deviation in the display.

The sums could also be generated with two passes through the set of input values but it should be clear how much more efficient the process is if one has the (M + x^{2}) function at one's disposal. Of course, once one moves to calculators such as the HP-45, TI-30, etc., which have summation functions then the process becomes easier and the machine counts the number of entries as well. One needs to evaluate the advantages of the Mathematician in the context of the time at which it was used.

The NS4615 Programmable offers the same features as the NOVUS 4510 plus a 102 step programming capability. The versatility of the programs which can be written is limited by the absence of conditional branches. I have not been able to demonstrate the programming capability with the device in my collection which has some internal damage due to leakage from the hard-wired rechargeable batteries.