 Three early models with this improved, continuous memory - the HP-25C, HP-29C, and HP-19C - actually had the words "" Continuous Memory "" printed in conspicuous, white script on the bottom margin of their faceplates.The "C" in the model designations was to distinguish those models within HP's calculator product line.HP did not print this phrase on subsequent, featured models because the novelty of continuous memory had by then faded and also because it could no longer claim it as a feature unique to HP calculators (Texas Instruments would later call their identical feature "Constant Memory").