Centring is very important for plotting detail through plane table surveying. Error in centring leads to error in plotting of location of objects. So, the operations involved in centring need careful consideration. On the other hand, plotting accuracy (Lesson 2) provides a limit within which no error gets perceptible in plotting. Thus, accuracy with which centring should be done depends on the scale of plotting and accordingly care in centering of plane table should be taken.

Thus, if S is the scale of plotting and 0.25mm is the minimum dimension of plotting, then 0.25 X S is the amount of error in field distance which may be allowed during centring without any effect on actual plotting.

For example, if the plotting scale is 1: 1000, then centring within 0.25 metre distance on ground can be permitted without any error in plotting.

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