This RPN calculator is handed from friend to friend and from parent to child across the generations, like a treasured heirloom that can also "produce all the valid IP header lengths".

From Danny's README:

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A simple RPN calculator. Orignally written by Mycroft [email protected].

I picked up this code in like 1996, and it's been passed around since then without a proper home.

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"help" command gives you list of commands.

Support for macros via a $HOME/.rpn_macros file. See rpn.macros in the repository for examples.