Topocad has three different types of transformation calculations. Helmerth and Affins transformations are calculated in Topocad drawing by pointing out points in the from and to system. Parameters are calculated and can be used directly, but also saved for later use. Parameters can then also be created for Gtrans which is the second transformation calculation.
Finally, the Proj4 transformation calculation, an open source method of calculation where all known coordinate system defined in EPSG can be transformed between each other.