This is the first time to use a caliper to make a precise measurement. A schematic picture of a vernier caliper is provided here.

To measure the diameter of a ball:

1. Put the ball between the jaws of the caliper.
2. Move the ball in the direction perpendicular to the caliper so that the spacing between the jaws can be just fit by the diameter.
3. Find where the Vernier Scale tick marks best line-up with the Ruler Scale tick marks. For example, look at the largest picture on that given sheet, the Vernier Scale 0.4 best line up with the Ruler Scale 2.5.
4. Then, first, we know that Y= 2.5(cm) and Y- X = 0.4 ´ (the whole length of the Vernier Scale from .00 to .00), where we can find the whole length of the Vernier Scale from the first picture, which is 0.9 cm. Therefore, X = 2.5- 0.4 ´ 0.9 = 2.14(cm).
5. Use the values you find from the best line-up of the Vernier Scale and the Ruler Scale.

Of course, you know 2 ´ Radius = Diameter.

Here, if you do things by the book, you should measure Length several times, establish a data table, and find SDOM of Length, s _Length. However, it always takes time to do so. Therefore, you may inspect the minimum scale of your vernier caliper or ruler, and take a reasonable guess about s _Length.

For instance, if the minimum scale of your Vernier Caliper is 0.01(cm), then you may guess that s _Length is possibly ± 0.005(cm) or ± 0.01(cm).

Be sure you understand how to use a Vernier Caliper because that definitely you will encounter it more than once during PHYS40A, 40B or PHYS2LA, 2LB, and 2LC.