Exact tidal study extends back to a fourteenth century record containing sexagesimal times. Earlier commentators have taken these times to be high water. This study shows they are for the later moment of when the flood ends; and, that eighteenth and nineteenth century elevation measurements formed a completely different way of considering the tide, leading directly to reliable predictions. The result shows the Thames tide to have been more consistent than previously stated; and consequently the actual change more accelerated. Therefore tidal current predictions are shown to have a longer history than have water surface elevation levels.
