A student investigated the refraction of light by a glass block. Figure 13 shows the protractor used to measure the angles of incidence and the angles of refraction. What is the resolution of the protractor used to measure the angles?

The resolution of a measuring instrument is the smallest increment on its scale. On the protractor shown, there are markings for every 10 degrees (e.g., 70, 80, 90). Between these markings, there are smaller, unlabelled lines. If you count the spaces between 70 and 80, you will find there are 10 divisions. This means each small line represents 1 degree. Therefore, the smallest angle the protractor can measure is 1°, which is its resolution.