There were at least eight hardware revisions of the HP-12C since 1981 (including one special issue). Over its lifespan, the proprietary silicon on sapphire HP Nut (originally the 1LF5, then 1LM2) processor's technology has been redesigned to integrate all the circuitry into a single chip (first the 1LQ9, then 1RR2) and to refresh the manufacturing process (as the foundry could no longer manufacture the necessary chips, having moved on to making higher-density chips). However, HP's market research found in the late 1980s that users did not trust results obtained too quickly and so the CPU speed was never improved from the original 884 kHz, but the speed could be increased by a user modification. In the late 1990s, the CPU was changed to a 3 V process (Agilent 2AF1-0001, later a Marvell 2AF1-0002) and the battery was therefore changed to a single CR2032 cell replacing the three LR44 cells previously used (F1637A).