Linear Measure

1 foot = 12 inches
1 foot = 0.3048 meter
1 mile = 5,280 feet
1 chain = 66 feet
1 mile = 80 chains

Area Measure               

1 acre = 10 square chains = ch²
1 acre = 43,560 square feet = ft² 
1 acre= 4,046 square meters = m²
1 square mile = 640 acres

Volume Measure          

You need to be practiced at performing unit conversions in the field. Jotting your unit cancellation table on paper, the back of an envelope, or whatever else might be available will help you be sure you are keeping the units straight. Problem solving in units that are familiar to fire staff is crucial to sound planning. Making a mistake with units can be very costly.

Precision is an indicator of how close the repeated measurements are to each other. The precision of a measurement refers to the smallest unit with which a measurement can be made.

Example 1 - Find the precision of Gabe's measured the length of hose connector: 2.1 ft, 2.2 ft, and 2.2 ft.

Step 1. Subtract the measurements from each other.
2.1 - 2.2 = -0.1

The precision of the measurement is ±0.1 feet.

Accuracy is a gauge of how close the measured value is to the true value. The accuracy of a measurement refers to the number of significant digits. See Section 1.6.

Example 1 - Gabe is measuring a length of connector hose. He measures it three times. The values he gets are 2.1 feet, 2.2 feet, and 2.2 feet. The actual value is 2.15 feet. How accurate are Gabe's three measured values?

Step 1. The accuracy of the measurements is the difference between the true value and the measured value.
2.15 - 2.1 = 0.05

The material in Chapter 9 focuses on various math and statistical terms, including accuracy, precision, average, and mean. The content includes discussions of range and standard deviation and how they related to measured values. Fire-related topics including planning and production rate are also presented.