Dark signal transfer plot. The median and standard deviation are computed for every pixel of a series of ten dark frames acquired on 31 July 2010 with T_i = 16.4 s and represented here as a two-dimensional histogram. A region on the left is dominated by the read noise, which amounts to about 10 ADU_15 bit rms. The shot-noise dominated region has a slope of 0.5 in the logarithmic representation. Above it, a significant proportion of pixels exhibit ten times more variability than shot noise. These are the hot pixels that suffer from RTS noise (cf. Sect. 1.3).