The first remarkable feature of the the SiPM statistics is the presence of discrete peaks in the histogram of charge collected in the SiPM(proportional to the SiPM signal (Volts) integral (Vs) by 1/Gain<sub>trans-impedance (V/A)</sub. This allows us to determine the charge collected per activated pixel (per photon) and therefore gives the gain of the device. This is the "self-calibration" referred to above.