COMB=4, FP-SPLIT=NO, and STEP-TIME=0.2. These minimum exposures can be reduced by half if COMB=2 is used and by a factor of four for COMB=NO. The complete expression for the minimum exposure time is:
where Nbackground is the number of background bins (col. 3), Nspectrum is the number of spectrum bins (col. 2), and ratio is from column 4. The minimum STEP-TIME is 0.2 sec.
You should specify your exposure time as an integral multiple of tmin.
