To simplify notation, the terms R side and V side are often used to designate the real side, where the light is traveling after it is reflected or refracted, and the virtual side, where the light appears to be traveling. For mirrors, the R side is always in front of the mirror, although the V side may change depending on the mirror and the position of the object.
The determination of sign for mirrors obeys the following conventions:
(1) o is positive when the object is on the R side, negative when the object is on the V side
(2) i is positive when the image is on the R side, negative when the image is on the V side
(3) r is positive for concave mirrors (center of curvature on R side), negative for convex mirrors (center of curvature on V side)
(4) f is positive for concave (converging) mirrors, negative for convex (diverging) mirrors
(5) m is positive when the image is rightside up, negative when the image is upside down
