<P> Microelectromechanical systems (or MEMS) barometers are extremely small devices between 1 and 100 micrometres in size (i.e. 0.001 to 0.1 mm). They are created via photolithography or photochemical machining . Typical applications include miniaturized weather stations, electronic barometers and altimeters . </P> <P> A barometer can also be found in smartphones such as the Samsung Galaxy Nexus, Samsung Galaxy S3 - S6, Motorola Xoom, Apple iPhone 6 smartphones, and Timex Expedition WS4 smartwatch, based on MEMS and piezoresistive pressure - sensing technologies . Inclusion of barometers on smartphones was originally intended to provide a faster GPS lock . However, third party researchers were unable to confirm additional GPS accuracy or lock speed due to barometric readings . The researchers suggest that the inclusion of barometers in smartphones may provide a solution to determining a user's elevation, but also suggest that several pitfalls must first be overcome . </P> <P> There are many other more unusual types of barometer . From variations on the storm barometer, such as the Collins Patent Table Barometer, to more traditional - looking designs such as Hooke's Otheometer and the Ross Sympiesometer . Some, such as the Shark Oil barometer, work only in a certain temperature range, achieved in warmer climates . </P> <P> Barometric pressure and the pressure tendency (the change of pressure over time) have been used in weather forecasting since the late 19th century . When used in combination with wind observations, reasonably accurate short - term forecasts can be made . 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), the greater the change in weather that can be expected . If the pressure drop is rapid, a low pressure system is approaching, and there is a greater chance of rain . Rapid pressure rises, such as in the wake of a cold front, are associated with improving weather conditions, such as clearing skies . </P>

What is above the column of mercury inside the glass tube of a barometer