It measures the minimum temperature in a day. Alcohol is used as thermometric liquid.
- There is a steel index inserted inside the capillary tube. Spring connected to the index prevents it from moving forward freely.
- With decreasing temperature, alcohol contracts and pulls the steel index along the capillary tube. The index will be left at the lowest position to which alcohol has contracted. Highest point of the index (concave meniscus of alcohol) reads the lowest temperature within the day.
- The index can be reset using a magnet.
Both the indicators are reset every 24-hour reading. It is commonly used by meteorological station to track daily fluctuations of temperature in a geographical area.