HP42s first major program (Double Integral) Best way to approach?

[Thomas Okken]

The HP-42S doesn't have expressions, so you'd have to write a keystroke program instead, like this:

Code:

00 { 40-Byte Prgm }
01▸LBL "FN"
02 MVAR "R"
03 MVAR "C"
04 MVAR "X"
05 RCL "R"
06 RCL "C"
07 X↑2
08 RCL "X"
09 X↑2
10 -
11 SQRT
12 ×
13 RCL "R"
14 X↑2
15 RCL "X"
16 X↑2
17 -
18 SQRT
19 ÷
20 END

HOWEVER... The HP-42S and DM42 don't support double integrals. If you try to use INTEG inside a function that is itself being integrated, you'll get the error message Integ(Integ).