Upper left:  Gain sensitivity versus PMT serial number.
Upper right: Rate effect at 5 kHz versus PMT serial number.
Lower left:  Voltage at gain of 500 A/lm versus gain sensitivity.
Lower right: Rate effect at 5 kHz versus gain sensitivity.

Colors denote different shipments from EMI.
Gain sensitivity is discussed in caption of Figure 1.
Rate effect is defined at Q(5kHz)/Q(0 Hz), where Q is the
charge measured from the PMT arising from a 10Hz reference
LED, and the rate refers to that of a background LED.