FUNCTION: sub3d PURPOSE: Takes two 3D structures and returns a single 3D structure whose data is the difference of the two. This routine is useful for subtracting background counts. Integration period is considered if units are in counts. INPUTS: d1,d2 each must be 3D structures obtained from the get_?? routines e.g. "get_el" RETURNS: single 3D structure CREATED BY: Davin Larson LAST MODIFICATION: @(#)sub3d.pro 1.10 01/10/08 Notes: This is a very crude subroutine. Use at your own risk.