Descriptions of stack in B3-34 family - MK-54, MK-56, MK-61 included - went like this: Imagine a stack with the following registers: T: 0 Z: 0 Y: 0 X: 0 X

Descriptions of stack in B3-34 family - MK-54, MK-56, MK-61 included - went like this: Imagine a stack with the following registers: T: 0 Z: 0 Y: 0 X: 0 X1: 0 The X register is the same as what you see on the indicator. There are 3 registers above X and one special register ("previous result") which is X1. When you enter digits, they go into X register, so pressing "1" "2" "3" leads to changes in X: X: 1 X: 12 X: 123 Now if you want to add another number to what you have in X, you have to somehow tell the calculator that you're done entering the number in X. The button for that was originally just "arrow up" (^) , later it became "B arrow up" (B^), when you press it, X gets copied to Y, previous Y content gets moved to Z, previous Z content - to T, previous T content is lost. So after "123" "B^" you have T: 0 Z: 0 Y: 123 X: 123 X1: 0 Now you may enter a new number in X; right after B^ newly entered digit will replace the content in X, and after that each additional digit will be considered a part of the number being entered. So, after "123" "B^" "56" you have: T: 0 Z: 0 Y: 123 X: 56 X1: 0 Now you can enter the operator - after you've already entered both operands, that's why it's "Reverse" Polish Notation (forward one is in e.g. Lisp lists). If you enter "+", you'll get: T: 0 Z: 0 Y: 0 X: 179 X: 56 So the "+" operator works on content of Y and X, Z gets copied to Y, T gets copied to Z and previous T content remains in T. X1 now has previous value - what was in X before operator, that is, 56. If you want to calculate 1 + 2 x 3, you enter 1 B^ 2 B^ 3 x + , and if you want to calculate (1 + 2) x 3, you enter 1 B^ 2 + 3 x . "x" here is "multiply". Notice you don't need to enter B^ again if what you have in X is the result of operator application, not just entered from the keyboard. There are commands X <-> Y, which swaps X and Y (and X also gets copied to X1), and "circular" (looks like "recycle" icon, which is triangular with 3 arrows, only this icon is round), which sends X to T (and X1), T to Z, Z to Y and Y to X. Four level deep stack is usually enough for many manual problems.