50g - Exponent of zero

[Joe Horn]

FWIW, the HP-71B gives you some control over what happens when EXPONENT(0) is executed, by setting the DVZ (DiVision by Zero) trap to 0 (bomb out with an error messasge), 1 (return the default value), or 2 (return the IEEE-suggested value):

TRAP(DVZ,0) @ EXPONENT(0) --> <beep!> ERR:EXPONENT(0)
TRAP(DVZ,1) @ EXPONENT(0) --> <beep!> WRN:EXPONENT(0) --> -9.99999999999E499
TRAP(DVZ,2) @ EXPONENT(0) --> <beep!> WRN:EXPONENT(0) --> -Inf

ERR messages persist in the display until you clear them. WRN messages only flash momentarily (duration is user-settable with the DELAY command).

EXPONENT(0) is such a special case that the HP-71 even assigns a unique error number for it (ERRN=3), which the manual explains as "Indicates attempt to compute the exponent of a zero argument. Sets DVZ (division-by-zero) flag (-7)."