The invention is an in-process calibration system. It is not an open loop system or a closed loop system, but a hybrid system that retains both the low propensity for error of the closed loop system and the simplicity of the open loop system. The invention comprises a housing, one or more robots that move in up to three axes mounted to the housing, at least one sensor for each axis of the robots' movement, and a microcontroller. The sensors are fixed to the housing at known locations, and the microcontroller instructs end effectors of the robots through a sequence of moves that intermittently trigger the sensors. When the sensors are triggered, the microcontroller corrects the idealized location of the end effectors in the microcontroller's calculations to the actual location of the end effectors, which is, at the moment that the sensors are triggered, the known location of the sensors.