Wednesday, 25 April 2012

Errors from markings Profile

A - Cumulative Errors - This is possible the most critical of the errors and is cumulative in nature. It affects the horizontality and accuracy of the datum line and building profile. While marking the datum using a spirit level and the string, only 2 points at a time could be  marked. So the method used, was marking a second point from a previously marked point, eg - from 1, '2' is marked and from '2', '3' is marked and so on. Also, due to the nature of the built profile, rarely a series of point could be marked from a single point or the main the primary base point. As a result apart from the first set of points in a space, other dimensions were all transferred using a reference point. The series of marking increased the probability of a cumulative error. While visually surveying the profile,before measuring, errors in horizontality of the datum line were noticed. 

B- Nature of Built profile - The built profile in parts were inaccessible, broken or narrow, especially at the corners, making it difficult to even hold the end of the string. As a result,  it was difficult to mark the datum line along such corners or areas or points accurately, affecting the overall level. 

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