The readback (Rdbk) indicates the currently set attenuation values. The Sreq indicates the manually requested values, and the Hreq indicates the automatically generated request. The Auto/Manual selection button determines the mode. In Auto mode, the peak goal value determines the attenuation such that the peak ADC value is about 90% of full range. The attenuation is set when injection starts up.
The "Atten Threshold" is the per-bucket value (in microamperes) at which a non-zero automatic attenuation is desirable. The formula in use is:
Attenuation = 20* LOG10 (Max_single_bucket_current/Atten_threshold)
The "Cal at zero Atten" is the bunch current calibration at zero attenuation. The initial guess at a bunch current calibration for an empty ring (no valid measurement available) is:
Calibration = Calibration_at_zero * exp(0.1151*Attenuation)
Where the Attenuation is either the automatically calculated or manually set attenuation, depending on the mode selected.