HP 39g+ - Manual (Page 154)

10-18 Using mathematical functions
SIGN Sign of value. If positive, the result is 1. If negative, –1. If
zero, result is zero. For a complex number, this is the unit
vector in the direction of the number.
SIGN (value)
SIGN ((x,y))
Examples
SIGN (–2) returns –1
SIGN((3,4)) returns (.6,.8)
TRUNCATE Truncates value to decimal places. Accepts complex
numbers.
TRUNCATE (value , places)
Example
TRUNCATE(2.3678,2) returns 2.36
XPON Exponent of value.
XPON (value)
Example
XPON(123.4) returns 2
Statistics-Two
These are functions for use with two-variable statistics. See
“Two-variable” on page 8-14.