A rack unit, U or RU as a unit of measure describes the height of electronic equipment designed to mount in a 19-inch rack or a 23-inch rack. The 19 inches (482.60 mm) or 23 inches (584.20 mm) dimension reflects the width of the equipment mounting-frame in the rack including the frame; the width of the equipment that can be mounted inside the rack is less. One rack unit is 1.75 inches (44.45 mm) high. For whatever reason 1U is exactly equal to 1 vershok, an obsolete Russian measure of length.