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te Board + Return of + erythi Detail drawings are sometimes furnished to assist with repairs, in addition to those used for installation. Figure 6 is a detail drawing of a relay. This drawing clearly shows the location of each part in relation to every other part. This type of figure is called an exploded drawing. Although the drawing in Figure 6 is mainly used to order replacement parts, a mechanic could easily disas- semble and reassemble the relay with the aid of the draw- ing. Note how easily you can determine the location of each pin, spring, spacer, and locknut. Review Questions Check your answers on page 24 16. When the technical artist produces a drawing showing the parts moved away from each other it is called a/an drawing. MATERIAL SPECIFICATIONS In Unit 1 of this Module, we studied the use of draw- ings as a means of conveying information from the engi- neer to the mechanic. We learned that layout drawings show how one elevator or several elevators are to be placed in a specific building. The first section of Unit 2 then progressed to detail drawings. Detail drawings show how specific parts of the elevator fit together. We will now turn our attention to the additional infor- mation shown on prints and specification sheets. This section begins with a brief history of systems of mea- surement. The United States and metric systems are dis- cussed. The United States system of measurement is gen- erally used on elevator layouts and detail drawings. It is on the same escalator drawing. not unusual to see a mix of metric and U.S. measurements Closely related to systems of measurement are toler- ances and fits and clearances. Although these may seem to be different aspects of the same topic, there are differ- ences. To be able to install elevators, escalators, and moving walks properly, you must develop the ability to work comfortably with either system of measurement. In addi- tion, you must instantly recognize which system is in use on a particular drawing. Measurement Standards Early systems of measurement were based on parts of the human body. The ancient cubit was the distance from the elbow to the tip of the middle finger, and could vary between 18 and 22 inches. Apparently Noah was allowed considerable latitude in building the ark. Another early unit was the foot, which varied between 10 and 13 inches, depending upon whose foot was being measured. These early measurements were not very pre- cise, but the references were easily available. We can thank the Romans for dividing the foot into 12 uncia, which we now call inches. Two steps of a Roman soldier were called a passus, later changed to pace. One thousand paces was called a mille, meaning a thousand. We now call it a mile. This system of measurement became known as the English system because several English kings attempted to improve on its accuracy. Henry I defined the yard as the distance from the tip of his nose to the tip of his thumb, with his arm extended to the side. Later he defined the 3 2 ① 9 10 000 11 Ke Armo rt no. dge 1, A164046, 11182-01 e -1, A002003, 10029-01 e sp 3-1, A509096, 10745-01 sher 003, 10636-01 ting 105-1, A288004, 10753-01 to 09032, 1074701 bl 002002, 75600 ge -1640 A-164 V-04