Is error comes when the line of sight does not coincide with the optical axis of theodolite.
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Collimation Error: Collimation error occurs when the collimation axis is not truly horizontal when the instrument is level. The effect is illustrated in the sketch below, where the collimation axis is tilted with respect to the horizontal by an angle α: Figure ( ) In this particular example, the effect is to read too high on the staff. For a typical collimation error of 20", over a sight length of 50m the effect is 5mm. If the sight lengths for back sight and foresight are equal, the linear effect is the same for both readings. When the height difference is calculated, this effect cancels: δh = (b + s. α) - (f + s. α) = b - f That is, the effect of the collimation error is eliminated if sight lengths are kept equal.
there are few types of errors in levelling...... these arr...... 1- instrumental error 2- collimation error 3- errors due to curvature and refraction 4- some other errors also
The span error is calculated by taking the span error and dividing it by the original measurement then multiplying by 100. The value gives us the span error as a percentage.
The same units as the mean itself. If the units of the mean, are, for example miles; then the error units are miles.
In the field of analytical measurement, the z-multiplier is a measure of error. It indicates a statistical probability of error. It is calculated using standard formulas for normal distribution.