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.