Hello,
I have been using Think or Swim for several weeks and I would like to add a filter to my options scan that would be a calculation of (ask-bid)/ask <10%. I cannot find anything in TOS that gets me to this. I see there is "Custom" feature and I am wondering if some of you who are familiar with this could give me guidance. If this is possible at all. Or is there a better way?

Thank-you

You can do this by writing a script and including it in the scan. If you are just looking for "penny-wide" spreads, TOS provides a filtering category called 'Penny Increment Options'