Most coastal dwellers live somewhere between the notable points at which predicted tides are published. And accurate local tides can be quite useful in determining when to go boating, fishing, sandbar walking, etc.
So for instance, I live in an area not too far from the San Francisco Golden Gate,
a well known landmark for which tide predictions are widely published.
But say, I wanted to know the tide at my local marina, or at the beach at my uncle's place? This involves making rough measurements, and guessing at the rest for height and timing of the tides and currents.
Most tide measurements seem to be made from buoys, which have some inaccuracy of postion due to fixed length tethers. Perhaps GPS has made this more accurate in recent years.
My idea is to take a small air pump, reservoir, and a thin plastic tube leading to a point below the lowest minus tide for the area. Then a simple servo-mechanism keeps the tube supplied with the minimal pressure necessary to bubble out a (fixed flow rate) small stream of bubbles.
The air pressure in the tube is then a measure of the "head" of water, i.e. the height of the tide. (it will take a higher pressure to keep flow fom the pump/tank at higher tides.) Operated rapidly enough, wave height could be measured as well.