Continued study of the time stability of a small water Cerenkov detector

This note describes continued studies at Fermilab of the long term stability of a small water Cerenkov tank. Previous results are presented for studies between November, 1997 and October, 1998. The data given here continue these measurements through December, 1998, when the tank and electronics were moved to a different location, and then to November, 1999. The water tank, bag liner, water, photomultiplier tube, and data acquisition software were unchanged for the additional measurements from June to November, 1999. However, some details of the geometry of the trigger counters relative to the tank and of the electronics may have differed. The setup for the 1999 results is described in this note. The same analog-to-digital converter (ADC) was used for both time periods. Its pedestal was quite stable during the 1997--1998 measurements, but sizeable changes were observed in the more recent runs. As a result, dedicated pedestal runs were performed, and a number of additional tests were conducted