With regard to land surveying what does the term "controls" mean?

with regard to land surveying what does the term "controls" mean? Any explanation of what the term "controls" mean and where/how it us used would be greatly appreciated! Cheers

With regard to land surveying what does the term "controls" mean?
control, is the start point and the point you refer to to check everything is where it should be. keep using it to check all readings are correct and haven't gone out. instrument error or you've knocked the machine, you can put it back using the control.