I have often thought it would be cool to build a relay calculator, along the lines of Casio's relay calculators that they marketed for a time in the 1950's before it became clear that electronics were the way to go. They even made some scientific and programmable machines, but a basic four-function machine with an accumulating memory register would be enough. Rick Bensene The Old Calculator Museum http://oldcalculator.com Sent from my Android phone using TouchDown (www.nitrodesk.com)