HP-67/97

Marketed as improved successors to the HP-65, the HP-67/97 were based on the technology of the "20-series" of calculators (HP-25, HP-19C etc.) introduced a year earlier. The two models are functionally equivalent, and programs on magnetic cards can be interchanged between them. The 67/97 provide a complete set of scientific, statistical and engineering operations, including trigonometric, logarithmic and exponential functions, coordinate conversions, average/standard deviation etc. The HP-67/97 series featured a program memory of 224 eight-bit words. The two extra bits per word compared to the HP-65's six allowed the designers to store any program instruction in a single memory cell ("fully merged keycodes") even if it required multiple keystrokes to enter. Programs could include 20 labels, subroutines (3 levels deep), four flag registers, 8 comparison functions, and extended index and loop control functions. At 15 digits, the display was wider than those of the predecessor models, although the decimal point was displayed on its own digit position. The HP-67 keys carry up to four functions each, accessed through "f", "g" and "h" prefix keys (gold, blue and black labels, respectively).