maximum minimum thermometer

The earliest, and still perhaps most familiar, form is the Maximum minimum thermometer invented by James Six in 1782.

He is noted for his invention, in 1780, of Six's thermometer, commonly known as the Maximum minimum thermometer.

A maximum minimum thermometer, also known as Six's thermometer, is a thermometer which registers the maximum and minimum temperatures reached over a period of time, typically 24 hours.

In 2006 S.Brannan & Sons Ltd, a UK company, was granted a patent for a mercury-free version of Six's Maximum Minimum Thermometer: instead of mercury two immiscible liquids are used supporting an index.