HP33S bug subtracting degrees from minutes?


Is the following a known HP33S bug?

Subtract ONE DEGREE from ONE MINUTE and you should get NEGATIVE 0 DEGREES 59 SECONDS. However, the HP33S returns NEGATIVE 0 DEGREES 58 MINUTES 20 SECONDS.

If you subtract ONE DEGREE from 4 MINUTES, you should get NEGATIVE 56 MINUTES, but instead, the HP33S returns NEGATIVE 55 MINUTES 20 SECONDS.

Am I doing something wrong?


>> you should get NEGATIVE 0 DEGREES 59 SECONDS

Sorry about the typo... I should have typed NEGATIVE 0 DEGREES 59 MINUTES 0 SECONDS...


The ->HMS function on the 33S has a bug; it does not always work correctly with negative numbers. It apparently can be trusted with positive numbers. This has been documented by HP in the "User's Manual Update" at


I programmed a simple "alternative" ->HMS function on my 33S, which is assigned to XEQ 5 (instead of right-shift 5). The "alternative" function checks to see if the input is negative. If it is, then it changes the sign, runs ->HMS, and restores a negative sign to the result. The program uses flag 4.

CF 4
x<0 ?
SF 4
FS? 4
FS? 4
CF 4

You should also be aware of the polar conversion bug, which is also documented in the "User's Manual Update"

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