Racks are vertically divided into regions, in height. Each region has three complete hole pairs on each side. The holes are centered at , , and from the top or bottom of the region. Such a region is commonly known as a U, for "unit", RU for "rack unit" or, in German, HE, for "Höheneinheit". Heights within racks are measured by this unit. Rack-mountable equipment is usually designed to occupy some integer number of U. For example, an oscilloscope might be 4U high. Rack-mountable computers and servers are mostly between 1U and 4U high. A blade server enclosure might require 10U.