Hi folks. As I found out in my research of the HP-71B system, there's a non-described function without arguments in the HP-71B ROM.
It's name is "MEMORY" and it returns the number 0 or one for unknown reasons. Maybe this is a check for HP, if the systems memory has been correctly implemented in this particular unit.
You can check it by just starting the system and entering "MEMORY". There are some other functions too: "MEMORY0" - "MEMORY9", but their reason is unknown til now. They all behave like "MEMORY"