Early 1980s 1982 I think, but the Museum of HP calcultors would tell you for sure. The HP41CX does too (and the timer module for the older HP41s includes the same clock chip, codenamed Phineas IIRC). I think the HP75 clock (like the clock in the HP71, and the one for the 41 series) is just an up-counter that counts pulses from a crystal and relies on software to turn it into time/date. Of course the Sharp PC1500 and Tandy M100 also have built-in real-time clocks (actual hardware chips that are read out in software). I remember clock cards for the Apple ][ (in fact I know I have one somwhere, it's got a NiCd PP3 battery stuck to it...) -tony