Most minimalistic (RPN) calculator

[Ross Barnes]

Fifty years ago I bought the NS 600 calculator for my mother. Since she used mechanical adding machines where the + key entered the first number the procedure for using this electronic calculator made sense to her and the two place fixed decimal point was adequate for checkbook reconciliation. It came with a trifold instruction pamphlet that she could refer to.

Padding with zeroes for division problems and keeping multiplicands and multipliers to three digits each kept you on the good side of the calculator. Slide rule skills needed for decimal point. The two level stack allows for easy squaring 111 + x gives 12321 not that she needed that function.