A 3m straightedge can be
used to check for plus and minus deviations from a datum. These 3m spaced
readings correlate to the reference grid.
A faster way to check the
flatness of large areas of a floor is to use digital surveying equipment such
as a profileograph.
The test is used to check compliance to certain standards; for example
in the UK, BS8204 – Part 2:2003 and in
the US, ASTM E1703 / E1703M.