DEPTH
Most chart depths are based on LAT (Lowest Astronomical Tide). This is the theoretical lowest low tide that can exist.
I said 'theoretical'. In most cases low tide will be always be a positive number, e.g.
+ ?.? and high tide + ?.?.
e.g. Low tide = +1.0m, High tide = +5.7m.
Very rarely low tide is a negative number, so the actual depth will be shallower than that shown on the chart.
Which if you are navigating a boat can be very dangerous.
Using LAT normally means that this danger is avoided.
TIME
You need to be careful with time. (At least in the UK).
UK Almanac's state time based on GMT (Greenwich Mean Time). But we have a time offset in the summer, BST (British Summer Time), of +1 hour.
So you need to ADD 1 hour to that stated in the Almanac (tide table). Some local (town) tide tables have the time quoted as BST during the summer, and GMT during the winter, to make things easier for tourists! TAKE CARE!!