Survey prims can be used with another electronic distance measurement (EDM) device to determine the distance of an object from a specific survey point, and they’re often attached to a prism pole so they can focus on a specific position. Corner cube prisms (also called “retroreflectors”) are often used for this type of measurement, and they will have some type of offset because the beam being transmitted from the device takes longer to leave the prism (especially from longer distances). This can be corrected by using a feature that accounts for this offset in relation to the plumb line of the surveying prism pole.