WFPC2 Instrument Science Report 94-02:
Observed WFPC2 Bias Jumps
April 13, 1994
Several unexplained jumps in the WFPCll bias levels have been observed since launch. These jumps can be observed in the image data as well as in the .xOD files (12 words of bias data).
The Complete Paper is available, (PDF, 0.2 MB).