The custom field list only shows up when you have selected Format = Custom. It is a list of check boxes for the columns you want to show on your report. This is a handy alternative to the "built in" formats such as "All" and "Short".
53,23. Use this filter to pick out certain bike model frames to compare. It works on the Id field. Pick two or more bike size ids from the list. Eg: To compare Surly Long Haul Trucker and Trek 520 in size 60, you would jot down the ID numbers "53" and "23".
Stack Range. (Minimum and Maximum stack). Use these two fields to specify the minimum and maximum Stack.
The min-max of the hypotenuse of stack-reach triangles. This is the single best indicator of the size fit of the bike. So it is an alternative to the "size" of the bike.
This filter allows you to find similar frame geometries based on Stack and Reach. You put in the stack and reach of some bike, and a tolerance such as plus or minus 20mm, and then you see the frames that fall within that range. The expression is just three numbers separated by commas. Eg: Stack,Reach,Tolerance. For example, to find all the frames similar to the Brodie Romulus size 60, you would put in: 626,410,20
This filter controls which columns show on the report. The key format is "custom" which allows you to pick whatever columns you want. "Custom" is a two step filter: first, select custom, and refresh the report. You now see additional filter checkboxes for every possible field. Check off the ones you want, and again refresh the report.
This filter allows you to sort the frame sizes in various orders. For example, sort by Stack, you see the frames with the maximum stack first.
WBase: Wheelbase. This is interesting to see the frames with the longest wheelbase. It is the Marin four corners. I note they also have the largest stack.