Allow 2 rectangle selections in same visual. Give quick comparisons between the two

Allow rectangle selections inside visuals, and provide a generic quick-summary (sum total, avr value etc) for the selection (via a tooltip or similar). Allow 2 selections at the same time in the same visual and provida a quick COMPARISON between the 2 selections.

Many times I look at timelines (lets say monthly).
very often I would like to quickly select a range in the timeline (eg: march - may) and get some quick facts for it (like sum total, avr value, etc). Now I would like to let that defined selection stay there, and select another period (like oct-dec) and get the same quick facts for that period. After the 2 selections have been made I want a quick comparison between the 2 periods giving me the numbers side by side and preferably the diff in % etc.

this would be extremely helpful when I want to quickly make an analysis of something