Fertility thermometer made by G H Zeal Ltd, London, in 2000. Measuring temperatures to an accuracy of 0.1oC, between 35 and 39oC, it is used to determine the date of ovulation on the basis that body temperature dips at this point in the cycle.

A fertility thermometer is used by women to determine the date of ovulation – the release of a ripe egg from the ovary – and therefore the optimum time for conception. Most women’s body temperature fluctuates approximately one degree after ovulation. She can assess when this has occurred by keeping a daily record of body temperature. This is the 'temperature method' of fertility control. The thermometer measures temperatures from 35˚C to 39˚. The thermometer was more accurate than other clinical thermometers of the time because it measured temperatures to within 0.1˚C. It was easily available from high street chemists.