[AugustH]

If the stations all used the same reference point, something unrelated to the actual tides, then I could see how this would work since you'd be comparing the apples to apples, but I don't think they do. The equation does have a 'datum' that's added to the output of summing all the harmonics, and this datum is not MLLW - it's more something to make the equation match the local conditions.

I'll do some research into the equation and the methodology behind it, but I'm not at all convinced that you can take two tide stations and compare them. If it was that simple, it would already be happening!