I was dusting off my old HP-42s and reviewing the owners manual when I came across a Q/A section in Section A. I tried to simulate the following question:

When I calculate the cube root of -27, I get a complex number (1.5000 i2.5981). Why?

The problem is that when I try the same thing I get "INVALID DATA" for a response. Why?

Hi Ross,

I think you may have the 42S set to calculate in REAL Mode only.

Go to MODES, then Down arrow, then see if you have CRES or RRES set. RRES gives real results only while CRES will allow for Complex Results.

Bill

Ross,

You can also just clear Flag 74. Flag 74, if set, will give Real Results only. See description for Flag 74 on Page 278 of manual.

Bill

Real RESults mode will allow complex results, but only from complex arguments. An operation on a real number that would require a complex answer will result in the "Invalid Data" message in Real RESults mode. If you enter the real number in complex form with zero as the imaginary component, the 42S will give a complex answer even in Real RESults mode. I think that Real RESults mode was included to provide compatibility with the 41C, which of course had no complex mode.

Thank you Bill & Jeff for your quick and accurate explaination of my problem. I have in fact changed the mode setting and that resolved my (non) problem. I had forgotten just how complex this great calculator really is.

Thanks again,
Ross