For your consideration, here is Tokos Medical Gestation Calculator Wheel and Risk Management Timetable, copyright 1987, no. PBM-00081, Rev. 2.  It has a diameter of 4 1/2 inches.  It turns fine.  It has some wear and creases on it.  It will be mailed in a bubble mailer with foam core stiffeners.  Item pictured is the actual item up for sale and comes from a non-smoking household.  (629.6a18b-.4ob)