It depends on how your data is structured. From your description it sounds like this should happen automatically - you click one measure and the other measure from the same row(s) in data is highlighted. You just need to create a highlight action from one sheet to the other.
Post sample data if you are having difficulties.
I think that may be my problem, ultimately - the data is contained in different tabs in the Excel spreadsheet I imported. Do I need to rework my source data?
Depending on the structure of the data, you may be able to join the tabs into a single data source and then it should work - just use multiple tables option when connecting, each tab is a table. Otherwise, re-working the data is the next best thing.