Why would I check “Use 0.1 Da Mass Step size”?

The 0.1 Da step size should be used whenever the peaks in the output spectrum are expected to be narrow, e.g., peptides and other molecules under 5 kD. With this option checked, ProMass will plot output data in the deconvoluted spectrum at 0.1 Da intervals.  If this option is unchecked, 1 Da intervals are used. Checking this box will cause your deconvolution to take longer, as more processing is required.