Idea 8of 22Builds onEstimate first, then measure
Count the spaces from the start
What if the object does not start at the end of the ruler?
Today you'll discover
- why the end mark is not the length
- how to count spaces, not marks
- how to slide it back to 0
Think firstA crayon from the 1 mark to the 8 mark
The crayon starts at the 1 and ends at the 8. How long is it?
Decide first, then press Next. Look at both ends of the crayon.
A crayon above a 12 cm ruler, its left end on the 1 mark and its right end on the 8 mark. A dashed line marks the start at 1, then numbered jumps count the spaces 1 to 7. Then the crayon slides back so it starts at 0 and ends at 7: from 1 to 8 is 7 cm. The last step shows a leaf from the 3 mark to the 9 mark.
See the whole ideathe big idea and the key word, in one place
The big idea
Line the start up with 0, or count the spaces from where it starts.
Easy to get wrongMany rulers have a gap before the 0. Line the object up with the 0 line, not the ruler's edge.
Why it happensA centimetre is the space between two marks. The mark only tells you where you are, not how far you have come.
Key word
- zero mark
- the 0 line near one end of a ruler, where measuring starts
Ready to use it?
- Measure an object that does not start at 0.