BOOK V . 142 measurement become a greater length than it should be , he sets upon the instrument a standing plummet level , the tongue of which , if the instrument is level , indicates no numbers , but the point from which the numbers start . … Compass . A , B , C , D , E , F , G are the seven waxed circles . When the surveyor has carefully observed each separate angle of the tunnel and has measured such parts as he ought to measure , then he lays them out in the same way on the surveyor ’ s field 20 in the open air , and again no less…
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