Which type of scale is used to measure an angle or to set off an angle and are marked on a rectangular protractor graduated from 0°-90°?

Explanation:

Understanding the Scale Types

Different types of scales are used in measurement tools, each serving a specific purpose. Here, we will evaluate the given options to identify which type of scale is used to measure an angle or to set off an angle and is marked on a rectangular protractor graduated from 0°-90°.

Analyzing the Given Options

1. "Chord scale." (Correct)

   • A chord scale is specifically designed to measure angles or set off angles. It is marked on a protractor graduated from 0°-90°.

2. "Diagonal scale." (Incorrect)

   • A diagonal scale is used for measuring small distances and is not typically used for setting off angles on a protractor.

3. "Plain scale." (Incorrect)

   • A plain scale is used for linear measurements and does not have graduations for angles.

4. "Vernier scale." (Incorrect)

   • A vernier scale is used for precise measurements of linear distances and does not apply to angle measurements on a protractor.

Conclusion

Therefore, the correct answer is Option 1: Chord scale.