GTCO CalComp, Inc. is a world leader in the design and manufacture of large-format digitizers, desktop graphics tablets, wide-format scanners used for a wide range of design, engineering, construction, graphics, GIS/mapping applications. The brand names manufactured by GTCO are CalComp, Summagraphics, and QuickRuler Estimat. Source Graphics sells and services all the GTCO brands as well as complimenting them with third party estimating software.