... For example, the distortion across the WF chips in WFPC2 amounts to ~2% at the chip corners, thus a commanded telescope offset of exactly 25 pixels at the chip center would create an additional 0.5 pixel shift at the edge of the detector. ... The current best-determined values of the projected pixel dimensions are stored in the Science Instrument Aperture File (SIAF), specifically defined for a single pixel at specified reference locations on the detector. ... pixels/side) . ... pixel) . ... WFPC2 ....