Payload-level testing. Top: bias image of the full 144 quadrants in the Focal Plane Array after processing to subtract mean levels. The greyscale bar is in analogue-digital units (ADUs) where the ratio of ADUs to electrons is the gain, so 1 ADU = 3.5 e⁻. Bottom: the readout noise per quadrant in the bias image for all 144 quadrants. Again, the colour bar is in ADU, so the readout noise in the worst quadrants is 3.8 e⁻, within the specification of 4.5 e⁻.