You really should not be using a Prayer Wheel (Nav Computer) in the Air! If I see one, I throw it in the back!
For a Diversion, a rule and pen is useful to draw a nice straight line, though not essential, and a Douglas Protractor to measure the track, thereafter everything else should be done by rule of thumb and estimation. From the end of your thumb to the knuckle is 10nm on a 1/2 mil chart.
A Douglas Protractor will fit into most kneeboards.