NOT Problem

[RhoSigma]

Your problem is not the NOT, but the AND, and you overlook only 1 AND 1 = 1.

Output 3:

(NOT 10) AND (NOT 15)

= (-11) AND (-16)

= (11110101) AND (11110000)

= 11110000 = -16

The last four bits result into 0s because only 1 AND 1 = 1, not 1 AND 0 and not 0 AND 1 either.