Now we take the table for the secondary port, Barfleur. At the top we have the times of high and low water, and the time differences. To the right we have the heights of high and low water, and the height differences. Let’s first calculate the time difference. 18:46 lies a little over half the interval between 15:00 and 21:00. Now we have to interpolate between 51 minutes and 44 minutes. The time difference for high water should then read 47 minutes. Then we add the minutes to 18:46 to equal 19:33. The high water in Barfleur will be at 19:33.