Калькулятор на FORTH для DM42 железа

IV42 has a slightly different approach to operate a scientific RPN calculator:

First - IV42 is FORTH orientated. It operates a big stack (actual 26 registers
from A to Z). Main part of FORTH is the dictionary, an alphabetical sorted
list of all commands and user programs. By the way the name IV or IVEE stands
for the roman number 4, which was also a reason for naming FORTH (4th
generation of programming languages).

The second and most obvious difference is the (very) big number display. IV42
shows the top of the stack (TOS) in an unusual big design. So it is possible
to operate the calculator under very bad light conditions.

The third difference are the 18 (!) function keys (3 rows of 6 top keys). So
you can fast and easy access commands, physical constants, unit conversions,
user programs or even ascii characters.

The fourth difference is, that IV42 always calculates with complex numbers.
Aside from all functions it is even possible to handle complex matrices or
complex hexadecimal numbers.

The fifth mentionable difference is the use of an exclusive ON/OFF key (EXIT)
like HP used it for the voyager series.

(source)