In summary:
There are three devices used in current measurement in the Hall. Once calibrated, the two BCM's are stable and linear over a wide current range. However, the BCM's, being cavity resonant devices are only sensitive to CW beam and so can not be bench calibrated with known current sources. Thus the BCM's are cross-calibrated with an Unser Monitor[1] (Direct Current Transformer). The Unser Monitor has been calibrated with known currents in wires, however, the ``offset'' on the calibration is noisy and the time average offset drifts in unpredictable ways. By measuring a series of currents over a short period of time, this drift can be minimized so that calibrations can be transferred to the BCM's.
The outputs of the front end electronics for these three devices are small voltages. These voltages are digitized by the use of V/F (voltage to frequency) converters. Scalers are used both in the control system (EPICS) and in the data acquisition to record these digitized signals.