inverse relationship between the height of the tide and atmospheric pressure is well understood (1 cm change in sea level for each 1 mb change in pressure) while the duration of slack water at a given location is inversely related to the height of the tide at that location. Misconceptions Slack water is a much misused term, often used to describe a period of equilibrium between two opposing streams when the water is anything but slack, but highly stressed. Although there may be no flow in either direction there may be many eddies, and since this so-called slack water occurs before high water while the tide is still rising, the tide may continue to rise even after the direction of the stream has reversed. Conversely, since it occurs after low water while the tide is rising, the tide may also continue to rise during this so-called low water slack period. Such conditions typically occur at river mouths, or in straits open at both ends where their entrances have markedly different physical characteristics. Examples include The Rip between Point Nepean and Point Lonsdale at the entrance to Port Philip Bay, Victoria, Australia; the Menai Strait between Anglesey and Wales; or the Strait of Gibraltar at the entrance to the Mediterranean Sea. Slack water may also be misused to refer to a process in caves. This occurs when a stream cave, or fluviokarst, is completely filled with water during flooding. Slack water is different from the 'stand of the tide', which is when tide levels 'stand' at a maximum or minimum (i.e., at that moment in time, not rising or falling). Dodge tides Some localities have unusual tidal characteristics, such as Gulf St Vincent, South Australia, where the amplitudes of the main semi-diurnal tide constituents are almost identical. At neap tides the semi-diurnal tide is virtually absent, resulting in the phenomenon known as a "dodge tide"—a day-long period of slack water—occurring twice a month; this effect is accentuated near the equinoxes when the diurnal component also vanishes, resulting in a period of 2–3 days of slack water. See also Stability theory, a main mathematical concept considering forces in equilibrium. References Tides Underwater diving environment