William Reis, age 16, of Meridian, Miss., for his question:

IN SURVEYING, WHAT IS A CHAIN?

A chain in surveying is a standard unit of length or measuring band that is equivalent to 66 feet, or 20 meters. A chain is subdivided into 100 links of 7.92 inches each, or 20 centimeters.

A mile has 80 chains, and an acre has 10 square chains.

The surveyor's chain is also known as Gunter's chain, after its inventor, the English mathematician Edmond Gunter, who lived from 1581 to 1626.

Surveying is as old as civilization. It started in ancient Egypt. Every year, after the Nile overflowed its banks and washed out farm boundaries, the Egyptians fixed new boundaries by surveying.

In engineering, a chain equals 100 feet (30 meters) or 100 links of one foot (30 centimeters) each.