monly used. Range-to-target distances are generally given in meters, longer distances in kilometers. Millimeters are frequently used to designate the caliber of a weapon. Because the units all differ by a multiple of ten, they can readily be interchanged and the choice of unit is frequently one of convenience.

(2) Both the gram and kilogram are often used. Again, the selection is one of convenience.

<3) Kilometers per hour are used for slow speed measurements, i.e. speed of vehicles, troops, and aircraft. Meters per second is used for faster speeds like the velocity of projectiles.

(4) Zero degrees centigrade <0° C) is the freezing point of water and one hundred degrees centrigrade (100°C) is the boiling point. The metric prefixes in a above are not used with temperature measurements.

2. Conversion Tables

1 in = 2.54 cm 1 ft = 30.48 cm 1 yd = 91.44 cm 1 mi = 1609.34 m

1 f t / sec = .305 m / sec ) ft /sec * 1.10 kmph I mph = 1.61 kmph one million one thousand one hundred ten one tenth one hundredth one thousandth one millionth d, Ttmptrttur*.

121 When converting degrees oentrigrade and degrees Fahrenheit, the difCerent starting polnu of the two scales must he taken Into consideration. The following conversion formulas make allowance for that.

°C « S/9<*F-32> •F « 9/5<#C»+32 (*) For example, to oonvert 77° F to can* trigrade:

•C ■ 5/9 (77—321 °C * 5/9 (451 °C * 25 (b) To convert 20° C to Fahrenheit t ®F » 9/5 (20) +32

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