How to read a minimum-maximum thermometer

Written by allan robinson
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How to read a minimum-maximum thermometer

A minimum-maximum thermometer measures the minimum and maximum temperature over a desired time period. This type of thermometer consists of a U-shaped glass tube filled with a liquid. The top half of the tube that records the minimum temperature contains alcohol; the top half of the tube that records the maximum temperature contains a vacuum or low-pressure alcohol vapour. As the alcohol expands in response to temperature changes, floats on both sides of the thermometer record the minimum and maximum temperatures.

Skill level:


  1. 1

    Examine the floats on the thermometer. The floats have some mechanism that will cause them to "stick" at their highest level until you press the reset button. The minimum and maximum temperatures are indicated by the bottom of the float.

  2. 2

    Read the scales on both sides of the thermometer. The scale on the minimum temperature side is upside down, such that the coldest temperature is at the top of the scale. The scale on the maximum temperature is like a regular thermometer.

  3. 3

    Record the current temperature with either side of the minimum-maximum thermometer. The temperature reading should be the same on both sides of a properly calibrated thermometer.

  4. 4

    Position your eyes so they are level with the surface of the liquid. If this is not possible while the thermometer is inside the storage unit, it may be removed from the unit briefly while it is read. In this case, avoid exposing the thermometer to your body heat while you read it.

  5. 5

    Reset the thermometer to use it for the next reporting period. After you have recorded the needed values, you can press the reset button. This will release the floats from their maximum positions so that they rest on the surface of the liquid.

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