So constructions will often have slight errors in them even with the most careful work. Nowadays, geologists are as likely to plot drawings on a computer as on paper. Nevertheless, the same geometrical principles apply. The accuracy of the construction is only as good as the computer input, and that in turn is only as good as the field measurements. So errors still occur and have to be dealt with.
Many constructions depend on finding the intersections of lines.
A small error in the location of one line will result in a large error in the position of the point when the lines meet at a small angle. Try to plan constructions so that lines meet at large angles. The larger you make your diagram, the less serious drafting errors will be. Drafting errors tend to be pretty much constant in size. Try to interpolate rather than extrapolate.