!) is given for the variance, then any pre-existing variance information is erased.
!) value is supplied, the new variance values are determined by the expression given for Parameter VARIANCE.
"DATA"implies normal error estimates, whereas VARIANCE=
"DATA + 50.7"might be used if a sky background of 50.7 units had previously been subtracted.
If a ‘null’ value (
!) is given for this parameter, then no new VARIANCE component will
be created and any pre-existing variance values will be erased.
All of the standard Fortran 77 intrinsic functions are available for use in the variance expression, plus a few others (see SUN/61 for details and an up-to-date list).
Calculations are performed using real arithmetic (or double precision if appropriate) and are constrained to be non-negative.
The data type of the VARIANCE component is set to match that of the DATA component.