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Hubble Space Telescope
What value should I put for NREAD in the Exposure Time Calculator?

Q.: What value should I put for NREAD in the Exposure Time Calculator?
A.: The number of reads of the NICMOS exposure time calculator refers to the number of MULTIPLE READS at the beginning and at the end of each exposure.

The MULTIACCUM readout mode, although it produces a set of non-destructive readouts, these are spaced in time; therefore, you'll end up having one read at the beginning and one read at the end of the exposure. Therefore for the readout mode MULTIACCUM, the NREADs is always 1.