If you live near sea the Tidegraph function, found on several G-Shock's and SeaPathfinders can be very handy. Where I live the difference between hight tide and low tide makes a difference of a 5m beach or a 100m beach. It is also handy for fishing.
First be sure you have tide. I once got a question from Istanbul how to set the local tide, but I believe the east part of the Middle Sea and the Agean Sea do not have a noticable tide (as all water has to come through the Street of Gibraltar).
If you live near sea, the tides are printed in the local news paper. There are probably also websites of the tides in important places. I took todays paper and looked for the high tide. I live near Vlissingen and the tide of Zoutelande only differs a few minutes. As there always are waves, an exact high or low tide are not very importand and programing a few minutes off will not be noticable when visualy observing the tide.
So high tides are at 10:25 and 22:51.
This was the easy part. Now you need to know when the moon is at the highest point, in other words, the time where the tide should be high. Due to land forms, the sun, rivers , etc the tide is often delayed. This can be a few minutes, in some cases almost 12 hours (I believe this is the case at the East Coast of the US).
To find out when the moon is at the highest point, I go to Time & Date World Clock. Sometimes weather websites also provide the information you want to know.
Look for the closest city and click on it. In my case it's Amsterdam:
If you live in Amsterdam, it's pretty easy, but I live roughly 200km south south west, but no problem.
Scroll down, until you see the coordinates. You see a link to "See other cities near Amsterdam". A new list opens. Choose here the city with the longitude cosest to you. In my case, Ghent (Belgium) is practically located 70 km south. When I click on that page I see this.
Now scroll down again for moon data:
You see that the Longitude is 3º 43'. I live at 3º36' (3.60º), so that's very near. The moon travels about 15º per hour = 0.25º (15') per minute across the earth.
The Moon is in the South at 21:25. This is also the highest point of the moon. Theoretical it would be high tide then. There is a delay, the Lunitidal interval, the real high tide is at 22:51. That's exact 1 hour and 26 minutes later. The Lunitidal Interval for me is 1:26.
This interval is of course different for other locations. Even in my small country there is much difference in Lunitidal Intervals.
I hope this helps you programming your Tidegraph.
Note that you have to set your watch to the right timezone and DST setting. If the summer time/Daylight Savings Time is changed, only use the DST ON/OFF feature to set correct time. In this case the Tidegraph will stay correct.
Artist Mike provided a link of tides in the UK with their interval:
Joakim Agren provided a link to a website that predicts tides on places all over the world. If you have a local table I think that's better, but this website can help if you too. I found that in Izmir (Turkey) there is a little tide (0.5 meter), probably hardly noticeable.