HMSCalc RPN 1.00 hmscalcrpn is a calculator that performs its operations in hours, minutes and seconds instead of integers or floating point numbers. Calculator operation is based on Reverse Polish Notation instead of algebraic notation. The calculator uses a four-value long integer stack to store interim results. A seconds-only mode may be toggled on or off. hmscalcrpn was written in object-oriented pascal, using the Free Pascal Compiler and the Lazarus IDE.