Q: Is it necessary to use a special thermometer for BBT?
A: A regular fever thermometer will do, but a special BBT thermometer is usually more reliable and more accurate. Many regular glass thermometers are only accurate to 0.2 degrees Fahrenheit, but you really need it to be accurate to 0.1 degrees.
Digital or glass?
The main benefit of the digital BBT thermometer over a glass BBT thermometer is speed. The BBT digital is more accurate for some people, and it only takes 30-60 seconds. This can matter if you are waiting to go to the bathroom first thing in the morning. The digital ones are harder to break and some may remember the temperature for you if you don’t want to chart it immediately.