About a fortnight ago I hung some new clocks in the kitchen. Yes, clocks plural, but not London/New York/Los Angeles. I sometimes work in a office where we have colleagues in New York and nobody gives a stuff about what time it is over there. One of the clocks is a conventional this-is-the-time-now clock with a big hand and little hand, in the approved fashion. No second hand, because those are just tedious irritants, but it does have a bonus day-of-the-week hand in case you wake up confused. Another clock is a moon phase clock. It takes 29 and a bit days or so to make one sweep of the clock face, marking out the phases of the moon from full through to new and back. The third clock is a tide clock. We bought as an amusement - you don't get much further from the sea than Birmingham - but I've found it to be the most involving timepiece I've ever owned.
A clock tells you the time now. If you're having breakfast, you already know more or less what time it is, but you might glance at the clock to see if you need to punt the kids off to school. If you had lunch a while ago, you know it's probably around 3ish, so you check the clock to see how much of longer you've got to hang around before you can knock off. You can't do that with a tide clock. The fact that the high tide is an hour away only tells you the high tide is an hour away. This time tomorrow, the high tide will be almost two hours away. The tides have a pattern, a rhythm, but it's not locked into our 24 hours in the day, tick-tock, clock work. A tide clock on your wall, or better the sea outside your window, gives a real feel for the passage of time, not as a series of discrete steps, but as a continuous, flowing motion.