The compact size, long battery lifetime and great quality made this calculator a big success in the eighties. The HP-11C is a mid range scientific programmable calculator. It also includs two new features: a built-in random number generator and a backspace key that allows numbers to be corrected a digit at a time. Non-Programmable Features Compared to the HP-10C, the HP-11C also includs: • Hyperbolic and inverse hyperbolic trig functions. • Probability (combinations and permutations). • Factorial, % change, and absolute value. • And, as mentioned above, backspace and a random number generator. Programming What really separates the HP-11C from its lower priced sibling is its more advanced programming capabilities. The HP-11C provids label addressing (0-9 and A-E), subroutines (nestable to 4 deep). 8 conditional tests, increment/decrement loops, and 2 flags. For program editing, the calculator features implied insert (instructions entered don't overwrite the current instruction) and deletion via the backspace key. The HP-11C provides indirection via a dedicated I register like the HP-34C. The I register itself is controlled by STOring or RCLing I and indirection is achieved by STOring or RCLing (i). Indirection is allowed on STO, RCL, GTO, GSB, the display modes and exchange (exchange X with the register indicated by i.) The I register can also be used with the ISG (Increment then Skip if Greater) and DSE (Decrement then Skip if less than or Equal.) The HP-11C has 63 lines of permanent program space. There are 20 registers (not including the I register) and each register converts into 7 lines of program space. Thus with all registers (except I) converted to program space, there are 203 program lines. User Mode The HP-11C includs a limited user definable keyboard. When the user mode is in effect (and the USER annunciator shows in the display) the gold shifted labels A-E are swapped with the unshifted math functions on the same keys. This allows 5 user programs to be invoked with single keystrokes.