Lesson 2 of 9
Reading the scale
Show on a big screenA glance seems to give the number. Counting the marks gives the right one.
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Step 1 of 4
- The scale is labelled 20 °C and 30 °C.
- Five small gaps sit between them.
- 30 − 20 = 10. 10 ÷ 5 = 2 °C per mark.
- The marker sits 3 marks up. 20 + 6 = 26 °C.
The rule
Marks are the small lines on the scale. The numbered ones are labels. A gap is the space between two marks. The difference is the bigger label minus the smaller label.
- Find the difference between two labelled marks.
- Divide by the number of gaps between them. The gaps are equal, so dividing shares the difference equally.
- That is what one mark is worth.
Count the marks the liquid is above the lower label. Add that many marks' worth to the label.
In the picture, the liquid is 3 marks up. Each mark is worth 2 °C. So 3 × 2 = 6 °C. Then 20 + 6 = 26 °C.
Watch out!
Do not read each mark as 1 °C. Here one mark is worth 2 °C. Counting 3 marks as 3 °C gives a wrong reading.
Try the lab to finish this lesson.