Tammy Feldmeier, age 14, of Gulfport, Miss., for her question:

WHAT IS A VERNIER?

A vernier is an instrument used to measure lengths and angles. It is named for Pierre Vernier, a French mathematician who invented it in the 1600s.

The most common vernier has a short graduated scale or ruler which slides along a longer scale. The subdivisions on the short rule are nine tenths as long as the subdivisions on the long scale. Nine small divisions on the large scale are equal to 10 on the small scale.

In using the vernier, the large scale is laid along the material to be measured, a small pipe, for example. The small scale is slid until it reaches the end of the pipe.

Now we check to see which of its divisions lines up with one of the divisions on the large scale. Suppose the five or fifth division on the small scale is one tenth smaller than the large divisions, five divisions are equal to only four and one half on the large scale.

Therefore, the end of the small scale rests at 25    4.5, or 20.5 on the large scale.

Engineers often use calipers with a vernier attachment.