Which Thermometer to measure BBT?

Why use a special thermometer to measure BBT?

The basal body thermometer is an ultra sensitive thermometer especially designed for use in natural family planning because the rise in basal body temperature that occurs after ovulation is very small and other thermometers would not be sensitive enough to pick up this small temperature increase.

The types of thermometer used in NFP

Two types of thermometers are used in natural family planning to measure BBT.

1. The basal digital thermometer which runs on a battery. It takes about one minute to reach body temperature using the digital thermometer.
2. The glass Geratherm basal thermometer which is an analogue device. This is a liquid thermometer which uses the liquid alloy ‘Galistan’ and which replaces the old mercury thermometer. It takes four minutes to reach body temperature.

What does the word ‘analogue’ mean? :

‘Analogue’ describes a device or system that represents changing values as continuously variable physical quantities. A typical analogue device is a clock in which the hands move continuously around the face. Such a clock is capable of indicating every possible time of day. In contrast, a digital clock is capable of representing only a finite number of times, for example, every tenth of a second. In general, humans experience the world analogically. Vision, for example, is an analogue experience because we perceive infinitely smooth gradations of shapes and colors.

What is the shelf life of these thermometers?

The shelf life of both the digital and liquid thermometers is life-long. However the battery may need to be replaced in the digital thermometers.

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Basal Digital Thermometers

The following two basal digital thermometers are recommend for NFP users:

• The ‘3M Nexcare Digital Basal Thermometer Accu-Beep, 524560’is manufactured by the 3M Corporation, Minnesota, USA and runs on a battery.
• ‘Geon Digital Thermometer to 2 decimal places MT-B231’ is manufactured by GEON Corporation, No. 12 Gung Ye Road, HSI HU, CHANG HWA HSIEN, TAIWAN.

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Analogue Thermometer – ‘Geratherm Basal Thermometer’ using Galinstan

The mercury-free cycle ‘Geratherm basal thermometer’ is manufactured by Geratherm Medical AG, Fahrenheitstrasse 1, 98716 Geschwenda, Germany. This thermometer is an analogue maximum thermometer (not digital) and does not require batteries. The measuring fluid ‘Galinstan’ in the glass capillary of the thermometer shows the measured body temperature on the temperature scale. ‘Galinstan’ is a liquid alloy of gallium, indiumand tin, it is completely non-toxic and environment-friendly. If a Galinstan thermometer is broken it can be disposed of with household waste. Galinstan thermometers now replace the old mercury thermometers as the mercury is toxic.