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e. A cen- decimal timeters ditional e of no you u- e 1 EXAMPLE 2 How many centimeters in one foot? We know there are 12 inches in a foot. We have also learned there are 2.54 centimeters in one inch. PUNCH IN THE CONVERSION FACTOR (2.54) ON YOUR CALCULATOR THE DISPLAY SHOWS: 2.54 NEXT PRESS X (to multiply) PRESS = THEN PUNCH IN THE NUMBER 12 AND YOUR DISPLAY SHOWS: 30.48. So one foot equals 30.48 centimeters. If we needed to convert that to meters, we'd just move the decimal point two places left. There are .3048 meters in one foot, which is another way of saying one foot equals .3048 meters. EXAMPLE 3 Using the results of the previous example, let's see how many meters in a mile. There are 5280 feet in one mile. PUNCH IN 5280 ON YOUR CALCULATOR THE DISPLAY SHOWS: 5280 NEXT PRESS X (to multiply) THEN PUNCH IN .3048 AND PRESS = YOUR DISPLAY SHOWS: 1609.344 One mile is equal to 1609.344 meters. To change to kilometers, move the decimal point three places left (smaller units to larger units). One mile is equal to 1.609 kilometers. To convert fractional parts of an inch to millimeters, you first need to change the fraction to a decimal. From Table 1, we remember 1/2" = .500 inches - how many millemeters is this? We know one inch equals 2.54 centimeters, but we want to find milimeters. We're going from larger units to smaller, so move the decimal point one place right. One inch equals 25.4 millimeters; now we can begin. EXAMPLE 4 PUNCH IN THE CONVERSION FACTOR 25.4 ON YOUR CALCULATOR THE DISPLAY SHOWS: 25.4 NEXT PRESS X (to multiply) THEN PUNCH IN .500 AND PRESS = YOUR DISPLAY SHOWS: 12.7 So there are 12.7 millimeters in ½ inch. Example 5 Let's check how many millimeters there are in 7/8". Looking again at Table 1, we see the decimal equivalent of 7/8" is .875. PUNCH IN THE CONVERSION FACTOR 25.4 ON YOUR CALCULATOR THE DISPLAY SHOWS: 25.4 NEXT PRESS X (to multiply) THEN PUNCH IN .875 AND PRESS= YOUR DISPLAY SHOWS: 22.225 So there are 22.225 millimeters in 7/8". Other fractional inch conversions are just as easy. Find the decimal equivalent of the fractions in Table 1 and multiply by the conversion factor. Some tool supply companies sell a low-priced plastic slide rule device to convert between U.S. and metric. You can find calculators for doing the conversion automati- cally. It can save a lot of time, and avoids mistakes. If you do a lot of this work, it's worth getting one. 9 Angles Angles are measured in degrees in both U.S. and Met- ric systems. In scientific work, angles are sometimes measured in radians, and you may encounter this in elec- trical modules. Degrees of angle are divided further into minutes and seconds. One degree contains 60 minutes. One minute contains 60 seconds. From this, one second equals 1/3600 of a degree. Escalator installation drawings often include angular dimensions because escalators rise on an angle. FITS AND CLEARANCES Fit refers to the clearance between any cylindrical part and the bore intended to receive it. A rotating shaft is smaller than the bore of its sleeve bearing. The difference between outside diameter of the shaft and inside diame- ter (bore) of the bearing is called the allowance, and in this case it is positive (+). When two parts are to be pressed together to rotate as one, outside diameter of the shaft is larger than inside diameter of the bore. This allowance is negative (-). Motor and generator armature shafts are an example of negative allowance. The American Standards Association (ASA) classifies eight categories of fits, numbered 1 through 8. Class 1 is