Post-manufacture variation of timing may be employed to address data-dependent degradation or creep in device characteristics affecting a differential circuit. The device includes a light source, a power source connectable to the light source and a mount attachable to the gun so that the laser is juxtaposed either the top surface of the gun or a side surface of the gun. A water distributor is coupled to the evaporator and configured to deliver water to the upper end of each ice-forming cell.