The rise and fall of a semidiurnal tide, from a plain running minute count. More...

#include <stdbool.h>
#include <stdint.h>

Macros
#define	TIDE_PERIOD_MIN 745
	The lunar semidiurnal period, 12h 25m. Two of these make one tidal day.

Functions
int	tide_level (int32_t minutes)
	How far in the tide is, from 0 at dead low to 100 at high water.
bool	tide_rising (int32_t minutes)
	Whether the tide is on its way in.

Detailed Description

The rise and fall of a semidiurnal tide, from a plain running minute count.

Tides run on the moon rather than the sun, so they come round every 12h 25m and drift about 50 minutes later each day. That drift is the whole character of a tide, and it is why this takes a continuous minute count rather than a time of day: a clock that resets at midnight would snap the water back every night.

This is a rhythm, not a prediction. A real tide table needs the port, the coastline and the lunar transit, none of which a watchface has. What it gives is water that moves at the right speed and never sits still, which is what the eye is actually reading.

Macros

Functions

Detailed Description