My assumption that the vol % in 10min is based on the previous vol % in 10 min was completely off but that's how the description seems to read. The problem is the description is hiding vital information on purpose. No idea what 400 is trading 4x normal more of what? The average X min interval? In how many days? Maybe, someone who's been using TI longer than me can chime in but if not I pretty much got an idea of how to use it. I'll just never know for sure how the formula is calculated.
I would ask in their own support-forum, if wanting to know. It seems to be active and well attended: http://forums.trade-ideas.com/