An external reference system, which allows a golfer to aim and control his body and swing alignment. Each heater element 10 is configured to heat a bubble forming liquid 11 in the printhead to a temperature above its boiling point to form a gas bubble 12 therein. The first series of substantially parallel V-shaped grooves define a first series of axes and the second series of substantially parallel V-shaped grooves define a second series of axes intersecting the first series of axes at an angle, thereby defining a plurality of pyramid-like spikes on the at least one portion of the ground engaging surface. The active pixel sensor comprises a feedback loop configured to receive the pixel voltage and control the integrator circuit to adjust the reverse bias voltage to substantially reduce the dark leakage current through the photodiode to a desired level. When the change of the image formation conditions is detected, the computation unit calculates the remaining time, based on the feed time per medium and the print time per medium after the change of the image formation conditions.