should be ok but covering it just in case
.
let us consider a normal number line
—|—|—|—|—|—|—|—|—|—|—
-4   -3  -2  -1    0   1    2    3   4   5
let us take 1
.                               x
—|—|—|—|—|—|—|—|—|—|—
-4 -3 -2    -1    0   1    2    3   4    5
.                                           x here i.e. 3
.                                x +1 +1
—|—|—|—|—|—|—|—|—|—|—
-4  -3 -2   -1   0    1    2    3   4    5
now we if we want to substract 2, we move in the opposite direction
. here which is -1
.                    x here
.                       -1 -1 x
—|—|—|—|—|—|—|—|—|—|—
-4 -3    -2 -1   0    1    2    3   4   5

similarly representing a hex number line
—|—|—|—|—|—|—|—|—|—|—
-4   -3   -2  -1   0    1   2   3   4    5

—|—|—|—|—|—|—|—|—|—|—
6    7   8    9    A   B   C   D   E   F

—|—|—|—|—|—|—|—|—|—|—
10  11  12 13  14 15 16  17 18  19

—|—|—|—|—|—|—|—|—|—|—
1A 1B 1C 1D 1E 1F 20 21 22 23 …

see 1 we add 2 so it is 3
see 9
we add 5 to it is
9
+1 makes A
+1 makes B
+1 makes C
+1 makes D
+1 makes E
——–
E
similarly minus we go back
but that is not very useful
123 h
342 h +
——–
we can do it as addition in decimal
but what if
12EF
5FAB
——
we resolve it column by column
1 |2|E|F
5 |F|A|B +
————
we convert F and B
15
11
—–
26
now now there cannot be more than 16 in any column
so we -16 (here 16 is the closest product of 16 i.e 16*1)
26
16 –
——-
10
and 10 is A
the 16 we minus here is carried over to the next column as 1

Supersebi3 :
B16 + B00B5
Sylver :
Supersebi3 :
CAFE + D00D
CAFED00D is a secret number for java or something like that

and
.
Supersebi3 :
Y u do b00b5 + b16 not b16 + b00bs
appinv :
same
Supersebi3 :
Ik
now if it overflows more than one
like
E
E
E+
—–
42
we do it like that
the amount to carry is 42/16
i.e. rounded
i.e. here 2
this is useful if you have to do much addition

now substraction
F0A6 – 842F
that was a way i found to be dead sure
without using those crazy tables for addition
if you have a simpler way, tell !