An apparatus including at least one processor; and at least one non-transitory memory including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus to: determine locations of at least two substrates on respective end effectors of the apparatus while the substrates are being moved by the end effectors in substantial unison towards respective target locations for the substrates; and while the end effectors are being moved towards the respective target locations, and based upon the determined locations of the substrates, adjust a position of at least a first one of the end effectors on the apparatus relative to a second one of the end effectors, where the position of the first end effector is adjusted relative to the second end effector while the apparatus is moving the substrates in substantial unison towards the respective target locations and prior to reaching the target locations.