Barometer Simultaneous barometric readings from across a network of weather stations allow maps of air pressure to be produced, which were the first form of the modern weather map when created in the 19th century. Isobars, lines of equal pressure, when drawn on such a map, give a contour map showing areas of high and low pressure. Localized high atmospheric pressure acts as a barrier to approaching weather systems, diverting their course. Atmospheric lift caused by low-level wind convergence into the surface brings clouds and sometimes precipitation. The larger the change in pressure, especially if more than 3.5 hPa (0.1 inHg),
Atmospheric pressure m is the maximum height to which water can be raised using suction under standard atmospheric conditions. Low pressures such as natural gas lines are sometimes specified in inches of water, typically written as "w.c." (water column) gauge or "w.g." (inches water gauge). A typical gas-using residential appliance in the US is rated for a maximum of 14 w.g., which is approximately 1048.37hPa. Similar metric units with a wide variety of names and notation based on millimetres, centimetres or metres are now less commonly used. Pure water boils at at earth's standard atmospheric pressure. The boiling point is the temperature