The telescope's operators perform monthly calibration tests to catalog these; with the WFPC's aperture closed a number of long exposures are taken, and pixels which differ significantly from near black are flagged.
Teleskopets operatører gennemfører månedlige kalibreringsprøver for at finde disse: Der tages et antal billeder, mens WFPC's åbning er dækket til, og de pixels, som afviger væsentligt fra næsten sort bliver markeret.