Distance Measurement Chapter 3 – McCormac’s 5 th

Historical Measurement Early Survey Crews Crew Chief Crew of 2 or 3 Brush Hogs Support Equipment Compass Chain – see page 42

Units of Measure Mile = 5280 feet Divide into 1/4’s, 1/16’s Chain: 66 feet -> 80 chains/mile 100 links -> 0.66 ft/link = 7.92” 20 Ch, 16Lk = Ch = feet Rod: 16.5 feet -> 4 rods/Ch, 320 rods/mi Engineers Chain – 100 feet Note Units – 10 th, 100 th of feet

Methods of Measurement Indirect Subtense Bars – pages Stadia – Chapter 14 EDM – Chapter 5 Direct Pacing Odometers/Wheels Taping or Chaining

Pacing (1/50) Try for natural pace Measure a known distance Pace a number of times, Average Determine: Length of Pace – nearest 0.1’ Number of Paces in 100’

Pacing Example Measured length = 215.0’ Pace 4 times – 74, 74, 75, 74 paces Average no. of paces = Length of pace = 215’/74.25 paces = 2.9’/pace Paces per 100’ = 100’/2.9’/pace = 34.5 paces

Taping or Chaining Equipment Needed Tape Steel Fiberglass Cloth Tensiometer Plumb bob Hand level Range Poles

Chaining Process Slope Chaining Measure along slope Convert to horizontal Plumb Chaining Measure with chain horizontal Downhill, when possible “Breaking” chain Forward Chainer (FC) reads 1/100ths Rear Chainer (RC) reads feet

Add vs. Cut Chains Add Chain – 1/100 th ’s forward from 0 RC at 71, FC at 0.54, record = 71.54’ Cut Chain – 1/100 th ’s back from 0 RC at 72, FC at 0.46, record = 71.54’

Chaining Process Establish Line Level chain Tension RC – sets full foot, calls “Mark” FC – sets 1/100ths, calls “Mark” RC calls feet – “86” FC – calls portion – “Point 23” RC repeats – “86.23”