There is minor typo in the current help file for Zemax OpticStudio. I caught it in the PDF for 2024 R1; however, it is present in the online help file from Ansys as well discussing Numeric Functions.
In the description of the obselete STDD() tag for ZPL programming, it references SRPO which does not exist. It meant to reference SPRO.
Confirmation that SPRO is correct can be found in
