The elusive negative zero on the HP 30b

[Marco Polo]

(05-10-2021 09:39 AM)EdS2 Wrote:  Back in 2012, Katie Wasserman noted something unusual:

Quote:Try -55555 ^ -55555 on your 30b and tell me what you see.

The correct answer is a very small negative number which on most calculators will be rounded to zero. In this particular case - and it seems the 20b doesn't do it - the result is a displayed negative zero, which even tests as unequal to zero, although arithmetically it behaves as zero.

My questions would be
- what other calculations will return a negative zero?
- how did Katie find this one?
- why does the 30b do this? (and why doesn't the 20b)
- do any other HP calculators do this, or have any similar oddity?

Thanks to Bob for checking the 20b behaviour.

- HP50g approx mode: 0 (flag -20 clear) or "Negative Underflow" (flag -20 set)
- HP50g exact mode: "integer too large"
- Free42 3.0.3 decimal (Win/Android): 0