RPN Calculator B3-19M

The application is based on a rather rare Soviet scientific calculator “Electronics B3-19M”, produced in 1975-1982. I used it as a student and for some time after, and retained the warmest memories of it.

The calculator uses reverse postfix notation, where the operation follows the operands rather than placed between them. This has certain advantages and conveniences. In particular, you don't need parentheses when writing expressions.

The calculator has three operational registers organized into a stack — X, Y and Z. X is the top of the stack, the main register, numbers are entered into it and the results are placed into it. When the stack is pushed, the value of Y goes to Z, X to Y. Operations on two operands X and Y push the result to X, and the value of Y is lost and replaced with the value of Z. Z is kept and can be used as a constant and to evaluate expressions with parentheses.
In addition to operational registers, the calculator has a special memory register Z.

Calculation examples:
1 + 2 → 1 ↑ 2 +
(1 + 2) * (3 + 4) → 1 ↑ 2 + 3 ↑ 4 + *

Entering a number with a sign, fractional and exponent parts:
-1.2e-4 → 1 . 2 |-| n 4 |-|

When you press the F key, the operation indicated above the key is performed:
exp(1) → 1 F exp

Trigonometric functions are calculated in radians.