Synthetic programming (HP-41)

Synthetic programming is an advanced technique of programming the HP-41C range of calculators, involving creating instructions (or combinations of instructions and operands) that cannot be obtained using the standard capabilities of the calculator.

Some HP-41C instructions are coded in memory using multiple bytes. Some of these sequence of bytes correspond to instructions the calculator is able to execute, but these cannot be entered in the program memory using conventional program entry methods (ie using the calculator as described in the user's manual.) Synthetic programming uses a bug in the calculator firmware to enter those byte sequences as a sequence of other instructions, then partially skipping halfway through the first instruction, so that the calculator believes the end of the first instruction is actually the beginning of a new one.