is the image number on which sky is to be determined
BOX=b
specfies VISTA box to do calculation in
Returns DAOPHOT's estimate of the modal sky value, or alternatively, an
iterated, 3-sigma rejected mean if the 3SIG keyword is given. It can be
instructive to compare these
with other VISTA estimates (
SKY,
WSKY). It is hard to get a good sky value!