A manipulator system comprising a column unit and a carriage supported by the column unit and configured to move along a desired axis of translation. A marker is provided on the column unit along the axis of translation. A sensor is associated with the carriage and configured to sense a position along the marker. A position display unit is configured to receive a position signal from the sensor and display a current position of the carriage along the axis of translation. In another aspect, the column unit defines at least one slot. A lock assembly is attached to the carriage and includes a tang axially moveable between an unlocked position wherein the tang is disengaged from the at least one slot and a locked position wherein the tang is engaged in the at least one slot.