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the independent check

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the independent check

the independent check is a teachnique of assurance . it is a means of guarding against a blunder or gross error and the principle must be applied at all stages of a survey . failure to do so will lead to the risk ,

if not probability , of , catastrophic failure , of the survey work . if obsevations are made with optical or mechanical instruments, then the observations will need  to be written down . A standard format should be used , with sufficient arithmetic checks upon the booking sheet to ensure that there are no computational errors . the observation should be repeated , or better , made in a different manner to ensure that they are in sympathy with each other. 

for example . if a rectangular building is to be set out, then once the four corners have been set out , opposite sides should be the same lengh and so should the diagonals. the sides and diagonals should also be related through pythagoras , theorem. such checks and many others will be checks should be applied to ensure that stations have been properly occupied and the observations between them properly occupied and the observations between them properly made. this may be achieved by taking extra and different measurements beyond the strict minimum required to solve the survey problem . an adjustment of these observation , beyond the strict minimum required to solve the survey problem . an adjustment of these observations , especially by least squares, leads to misclosure or error statistics , which in themselves are  a manifestation of the independent check.

data abstraction, preliminary computations. data preparation and data entry are all areas where tran- scription errors are likely to lead to apparent , blunders . ideally all these activities should be carried out by more than one persson so as to duplcate the work and with frequent cross - reference to detect errors. 

in short , whereever there is a human imteraction with data collection there is scope for error. every human activity needs to be duplicated if it is not self- checking . whereever there is an opporunity for an error there must be a system for checking that no error exists. if an error exists there must be means of finding it .