Band saw back gauges measure the chord height (distance from the center of an arc to a straight edge) over a set distance. Usually, this chord height is expressed in a fraction of an inch in 5 feet. The most frequently used "back" is 1/64" in 5 feet.

The following chart shows the reading various lengths of back gauges will give on the same saw. To use this chart:

1. Determine the decimal equivalent of the desired chord height (the decimal equivalent of 1/64" is .0155", 1/32" = .031", 3/64" = .047");
2. Read down the chart under the column for the known chord length (e.g.: 5 ft) to find the known the chord height (e.g.: .0155");
3. Read across the chart to find the equivalent reading on a gauge (or chord) of a different length.

For example, to determine the readings on a saw with 1/64" back in 5 ft, read down the 5 ft gauge column to the line with the decimal equivalent of 1/64" (.0155"). A 4 ft gauge will read .010" and a 3 ft gauge will read .0055" on this saw.