HP 42S - Manual (Page 31)

11 Other Bases
To work with other bases we must use the ▀ BASE menu (over the “4”).
This menu has the following functions:
A...F: Select hexadecimal mode and show A to F.
HEXM: Select hexadecimal mode.
DECM: Decimal mode.
OCTM: Octal mode.
BINM: Binary mode.
LOGIC: Show the logic functions AND, OR, XOR, NOT, BIT?, ROTXY.
Example: How do we write 500 in hexadecimal mode?
Solution: In decimal mode enter 500 and then select HEXM. You will find 1F4.