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Is Sharp PC-1002 the oldest calculator than it uses interchangeable rom? 

"Most novel among recent calculator developments is the AC-powered desk-top PC-1002 from Sharp Electronics Corp., Paramus, N.J. Intended for engineering applications, this Japanese-made machine performs 15 scientific functions. In addition, this calculator offers up to four individual programs or a total of 256 steps which are controlled by four special keys (A, B, C, D). A plug-in programmable read-only memory (PROM) module contains the commands. When installed, the PROM becomes part of the calculator's hardwired system. With different PROMs, the functions of the special keys are changed, converting the calculator to user-specified applications.

Standard chips are now available for statistics, mathematics, metric conversion, and surveying. Additional chips covering structural engineering, electrical engineering, finance, and other fields are currently in preparation.

Apart from the PROM function, the PC-1002 can be keyboard programmed up to 64 steps. The 15 functions provided by this calculator include trig, inverse trig, hyperbolic, exponential, logarithmic, factorial, power, azimuth, and area calculations. The unit offers ten-digit mantissa, two-digit exponent, and eight memory registers. Exponential display capacity is from 10-99 to 1099 and zero. Model PC-1002 weighs 1.2 kg and costs $645, including one standard PROM chip. Sharp will design and manufacture special PROM modules to order. There is an additional design charge for custom-made chips."


SHARP PC-1002

Would anybody have those ROM'S to do a donation for me to complete mine PC-1002? :-)

Definitely not the earliest but probably the most famous machine in this respect is the TI-58/59 series. Other machines that come in to my mind are the home computers from Atari and CBM. I think, they were all 4 years or so younger than your example.

Think about the Diehl Combitron.
http://boris.jakubaschk.name/computergeschichte/ecomp/combitron.htm

It used exchangable metallic ROM strips.

HP 9805A desktop calculator, circa 1974. Interchangeable modules which included both ROMs and function keys.