You figure out the focus point for each filter from a base line. Like, I use my L filter and it focuses at step 3000. My red filter is at 2975. My blue filter is at 3025. I put those numbers in the filter dialog. I tell SGP to focus with my L filter. But, today the L filter focuses at 3010. It will offset to 2985 when I switch to my red filter.
Make sense?