RCW 58.20.205: Datum conflicts.

The provisions of this chapter may not be construed to prohibit the appropriate use of other datums, other geodetic reference networks or systems, or other plane coordinate systems. Any other such datums, networks, or systems used must comply fully with the information requirements for the Washington plane coordinate system. This includes, but is not limited to: The source of the datum, network, or system; metadata of the observations; factor used to convert from meters to feet; and combined factors applied to land boundary lines used in land surveys or deeds to compute ground distances or areas.