Registers that contained intermediate results or other codes related to pending operations were accessible in several Texas Instruments calculators. On the SR-52, these registers were explicitly numbered and could be accessed through the STO and RCL keys. On the TI-58/59, they were more hidden; access was possible through the undocumented HIR instruction, which had to be "synthesized" in program memory. On the TI-88, these registers were well documented, and accessing them was possible under program control through synthesized instructions described in the manual. Sadly, on later models such as the TI-66, access to these registers was explicitly disabled, along with the ability to synthesize undocumented instruction codes in program memory.

The following is a list of the TI-88 hierarchy registers: