A device for controlling displacement of a syringe piston comprises a handheld casing, first and second engagement means. The first engagement means is formed exteriorly of the casing to engage the syringe's finger flange. The second engagement means slides on a first axis relative to the casing and engages the thumb rest. The device comprises means within the casing to cause the second engagement means to move along the first axis, causing the piston to move outwardly. An electronic controller module for controlling outward movement of the piston comprises an input/output port and a processor module. The processor module determines a prescribed movement speed and sends a motor command via the port at an initial motor speed. The motor causes the outward movement. The port receives speed measurements. The processor module attempts to match the measurements to a prescribed speed by sending successive motor commands via the port.