An injection unit includes a cylinder casing comprising an inner cylindrical surface extending along an axis, and a piston housed in the casing and translatable along the axis between an advanced and a retracted position. The piston includes a piston radial surface in facing relation to the inner cylindrical surface, and the piston radial surface has a measurement detection feature. A probe is fixed relative to the cylinder casing, the probe communicating with the measurement detection feature when the piston is in and moving between the advanced and retracted positions to measure the translation of the piston.