Radio Shack TRS-80 PC-3 Owner's Manual page 56

Thus, 1 is inverted to 0, and 0 to 1 for each bit, which is "to take negative (NOT)."
Then the following will result when 1 and NOT 1 are added together:
0000000000000001 (1 )
+)
1111111111111110 (NOT 1)
1111111111111111 (-1)
Thus, all bits become 1. According to the above number list, the bits become -1 in deciml notation; that is, 1 + NOT 1
==
-1.
The relationsh ip between numerical value X and its negative
(NOT X) is:
X
+
NOT X =-1
This results in an equation of NOT X = -X-1
i.e.NOT X==-(X+1)
From this equation, the following results are found
NOT 0=-1
NOT-1=0
NOT -2 = 1
More than two relational expressions can be combined with these operators. You should take care to use parentheses to make the
intended comparison clear.
(A<9) AND
(8)5)
(A>
=
1'1)
AND NOT (A>
201
(C
=
5) OR (C = 6) OR (C
=
7)
54