To sum it up for myself :
Ab vrbe condita (AUC or a.u.c. or V.C. or u.c. (as used in
DRC) is Latin for "from the founding of the city" (of
Rome), supposed to have happened in 753 BC. as initiated by Varro.
So to convert this date into BC and AD
for V.C. dates lower as 753 => (753 - V.C.) +1 = B.C. for example: V.C. 692 would be (753 - 692) +1 = 62 B.C.
753 V.C. itself => 753 = 1 B.C.
for V.C. dates higher as 753 => V.C. - 753 = A.D. for example: V.C. 775 would be (775 - 753) = 22 A.D.