TWJCalc 1.02 written by Phill van Leersum running as an applet.  For more features (eg save/load) download the standalone version from SourceForge

If you find this useful, please tell me.  Similarly, if you find a defect, please tell me.

With many thanks to Daniel Binngamon and Pete Kosel for allowing me to copy their algorithms. 

There is a test version of TWJCalc with a 'thumb hole' calculation.