I had the SR-51 first ( non-programmable). Useful, but I was not allowed to use it at work- the use of calculators was forbidden in the Cyclotron lab (University of Maryland Sectored Isochronus Cyclotron Lab, UMSICL http://accelconf.web.cern.ch/accelconf/p69/PDF/PAC1969_0438.PDF), as the radiation levels would supposedly fry them. Had to use a slide rule there.