I've been meaning to scan this chart myself, ever since I first saw it photocopied in the class packet for Lee Patterson's Canterbury Tales class, but someone saved me the trouble (via BoingBoing). It's a handy flowchart from James A. Brundage's book Law, Sex, and Christian Society in Medieval Europe that summarizes when its safe (theologically speaking) for one to have sex in the Middle Ages. Here's the link to the Flickr post.

I know flowchart humor is all the rage lately, so you'll want to see it its full glory, but here's a transcription of the questions:

--Feeling Randy? Yes: continue. No: Stop! Sin!
--Are you married? Yes: continue. No: Stop! Sin!
--Is this your wife? Yes: continue. No: Stop! Sin!
--Married more than three days? Yes: continue. No: Stop! Sin!
--Is wife menstruating? No: continue. Yes: Stop! Sin!
--Is wife pregnant? No: continue. Yes: Stop! Sin!
--Is wife nursing a child? No: continue. Yes: Stop! Sin!
--Is it Lent? No: continue. Yes: Stop! Sin!
--Is it Advent? No: continue. Yes: Stop! Sin!
--Is it Whitsun week? No: continue. Yes: Stop! Sin!
--Is it Easter week? No: continue. Yes: Stop! Sin!
--Is it [any other] feast day? No: continue. Yes: Stop! Sin!
--Is it a fast day? No: continue. Yes: Stop! Sin!
--Is it Sunday? No: continue. Yes: Stop! Sin!
--Is it Wednesday? No: continue. Yes: Stop! Sin!
--Is it Friday? No: continue. Yes: Stop! Sin!
--Is it Saturday? No: continue. Yes: Stop! Sin!
--Is it daylight? No: continue. Yes: Stop! Sin!
--Are you naked? No: continue. Yes: Stop! Sin!
--Are you in church? No: continue. Yes: Stop! Sin!
--Do you want a child? No: Stop! Sin! Yes: GO AHEAD! But be careful: No fondling! No lewd kisses! No oral sex! No strange positions! Only once! Try not to enjoy it! Good luck! And wash afterwards!

It's funny. I never considered James Brundage to be the sort of historian who'd use so many exclamation points so cavalierly. Those wacky canon law experts.

Also, I found a handy summary of the book from whence the flowchart was lifted here