Definition
Compare the day's range at the reference port with the port's mean spring and mean neap ranges and interpolate the tabulated spring and neap rates in the same proportion. If springs give 3.0 knots and neaps 1.4 knots, and the day's range lies halfway between mean neap and mean spring, use about 2.2 knots. Admiralty Tidal Stream Atlases include a computation of rates diagram that performs this graphically.
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