Idea 7of 24Builds onA degree is a tiny turn
Put the protractor on the vertex
Where does a protractor go to measure an angle?
Today you'll discover
- where the centre mark goes
- which line sits on an arm
- where to read the number
Think firstAn angle to measure
Where does the small mark at the middle of the protractor's straight edge go?
Decide first, then press Next. Find the little cross at the middle of the straight edge.
An angle of 40° with its vertex near the bottom middle. A half-circle protractor slides up onto it, its centre mark on the vertex and its straight edge along the right-hand arm. The spot where the other arm crosses the scale is ringed, and a curved arrow counts up from 0 to 40. The last step shows an angle of 120°.
See the whole ideathe big idea and the key word, in one place
The big idea
Put the centre mark on the vertex and the 0 line along one arm, then count up.
Three stepsCentre mark on the vertex. The 0 line along one arm. Read where the other arm crosses, counting up from that 0.
Easy to get wrongIf the arms are too short to reach the numbers, make one longer with a ruler first. Longer arms do not change the angle.
Key word
- centre mark
- the small mark at the middle of a protractor's straight edge; it goes on the vertex
Ready to use it?
- Measure an angle with a protractor.