How to Use a Protractor
⏱ 0:26📘 Grade 4 · Measuring angles
Two things must line up: the centre on the vertex and the zero line on one side. Then read from the zero you started on: 60°, not 120°.
The videos are narrated in Mandarin Chinese with on-screen subtitles.
📚 What you will learn
- Put the protractor’s centre on the vertex of the angle.
- Line up the zero line with one side of the angle.
- Look where the other side crosses the scale, and read the scale that starts at 0 on your side.
- A protractor has two scales (inner and outer); reading the wrong one gives 120° instead of 60°.
🎙️ What the video says (in Chinese)
- 用量角器量角，该怎么放、怎么读？记住：两个重合！
- 第一：量角器的中心点和角的顶点重合。
- 第二：0 刻度线和角的一条边重合。
- 再看另一条边对着几度。这条边对着内圈的 0，就读内圈：60°，不是 120°。
- 点对点，线对线，从 0 开始读度数！
✏️ Try it yourself
The side lies on the outer scale’s 0 and the other side points to 40 on the outer scale. How big is the angle?
Show answer
40°
Is an angle bigger if you draw its sides longer?
Show answer
No. The size depends only on how wide the sides open.
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