SURVEY PRINCIPLES: PRINCIPLE OF CONSISTENCY

Any ‘product’ is only as good as the most poorly executed part of it. It matters not whether that ‘product’
is a washing machine or open heart surgery, a weakness or inconsistency in the endeavor could cause a
catastrophic failure. The same may apply in survey principle, especially with control. For example, say the majority
of control on a construction site is established to a certain designed precision. Later one or two further
control points are less well established, but all the control is assumed to be of the same quality. When
holding-down bolts for a steelwork fabrication are set out from the erroneous control it may require a good
nudge from a JCB to make the later stages of the steelwork fit.
Such is the traditional view of consistency. Modern methods of survey network adjustment allow for
some flexibility in the application of the principle and it is not always necessary for all of a particular
stage of a survey to be of the same quality. If error statistics for the computed control are not to be made
available, then quality can only be assured by consistency in observational technique and method. Such a
quality assurance is therefore only second hand. With positional error statistics the quality of the control
may be assessed point by point. Only least squares adjustments can ensure consistency and then only if
reliability is also assured. Consistency and economy of accuracy usually go hand in hand in the production
of control.