Reading a thermometer scale

A 15-cm ruler can measure down to 1 mm. What is the smallest value a thermometer can read? Here is how to find it:

• Pick two bigger marks next to each other and see how many degrees apart they are.
• Count the small divisions between them.
• Divide: degrees ÷ number of divisions = value of one small division.

On your book's thermometer, the bigger marks are 0 °C, 10 °C, 20 °C and so on: 10 °C apart, with 10 small divisions between them. So one small division = 10 ÷ 10 = 1 °C. The smallest value it can read is 1 °C.

Other thermometers differ:

• 10 °C apart with 5 divisions: 10 ÷ 5 = 2 °C per division.
• 10 °C apart with 20 divisions: 10 ÷ 20 = 0.5 °C per division. Only a thermometer like this has a mark exactly at a value such as 22.5 °C.

Reading it: find the mark the top of the liquid column reaches. Start from the bigger mark just below the top and count up the small divisions, adding one division's value each time.

Thermometers are not all the same: the one in your school may have a different range and a different smallest division. Always look carefully at the one you are using.