The tidal prediction for Drummonds is just that, a well educated guess based on years of observed data. Many factors will affect the tide tables at Drummonds including local winds and pressure systems. A margin of error of at least 10 minutes is to be expected with any forecast and its this level of accuracy we aim to achieve. Data quality varies by port and country: large western commercial ports will be very accurate, small Asian fishing villages are probably going to be somewhat less accurate. If you think the tide tables at Drummonds are wildly innacurate please let us know (please tell us what source you are comparing us with).