OK so this is an amazing blog dedicated to blackboards in porn & examining the formula on the featured board. Look forward to more from whichever maths geek clearly spends too much time on Red Tube (now that site could not be more NSFW hence no link).

Via Nerdcore

Celebrating pornographers who go the extra mile when set dressing classroom porn and actually write something on the blackboard. What do they write, and is it correct?