How a gestogram works

Using the gestogram is very simple, but in order to use it, the woman must know the date of her last menstrual period (LMP). The woman can turn the small wheel of the gestogram until the mark with the text FUR (or equivalent) on the large wheel coincides with the corresponding date on which she had her last menstrual period before becoming pregnant.

Once this is done, without moving the gestogram wheels from this position, any marks on the small wheel (such as weeks of pregnancy or likely date of delivery) can be related to a date on the larger wheel.