This is also a type of Autocollimator, there is an illuminated reticule in the focal plane of the collimating lens. This illuminated reticule is projected as a parallel beam by the collimating lens which after striking a polished surface or reflector below the instrument is refocused by the lens in the field of view of the eyepiece. In the eyepiece there is another/reference graduated reticule fixed. The reflected image of the illuminated reticule is received at cube beam splitter to the fixed graduated reference reticule. Thus, the changes in angular position of the reflector in two planes are indicated by changes in the point of intersection of the two reticules.​