Quote:

"SigmaREG?" which should return the number of the statistical registers...

Thomas' answer is correct, but you misdescribed the function. "SigmaREG?" returns the identifier of the __first__ of the six numbered registers used for statistical summation. The user can set that register using "SigmaREG". The HP-42S retained both functions, perhaps for compatibility with the HP-41. However, the "HP-42S' little brother" HP-32S designated stat registers in a *better* way: the six stat registers are taken from the free memory pool.

For statistical summation, earlier models use the lowest-numbered registers (last to be de-allocated for programming), except that the HP-15C used R2 through R7, reserving R0 and R1 for matrix indices.

There is a similar function called "SIZE?" which supplements SIZE on the HP-41. SIZE? returns the number of registers allocated to data storage, which is settable by SIZE. SIZE?, however, __is__ available on the X-Functions module as well as the HP-41CX.

Here's yet another example where the HP-15C trumped the HP-41C/CV: The equivalent of SIZE? was available on the HP-15C as "RCL DIM (i)".

-- KS

*Edited: 5 Oct 2007, 3:25 p.m. *