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Distance Between Two
Points
Pacing
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Standardisation
Catenary
Slope
Tension
Tachaeometry
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Measurement of
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Theodolite
Tachaeometry
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Electronic Tachaeometry
Catenary (Sag)
If the tape cannot be supported for its length then it will hang freely under the influence of gravity. The shape the tape will take is known as a catenary and can be determined mathematically.
The correction is:
| DL = | -( Mg )2l3 | or, for steep slopes, DL = | -( Mg )2l3 | cos2b |
| 24T2 | 24T2 |
For example, for a catenary of 30m, a tension of 50N and a mass per unit length of 0.011kg/m;
| DL = | -( 0.011 x 9.8 )2 x 302 |
| 24 x 502 | |
| = | 0.005 m |
The tension must be measured with a spring balance for this correction to be determined.