Weather map motion. Two-dimensional streamlines based on wind speeds at various levels show areas of convergence and divergence in the wind field, which are helpful in determining the location of features within the wind pattern. A popular type of surface weather map is the surface weather analysis, which plots isobars to depict areas of high pressure and low pressure. Cloud codes are translated into symbols and plotted on these maps along with other meteorological data that are included in synoptic reports sent by professionally trained observers. The use of weather charts in a modern sense began in the middle portion of the
Moody chart (Pa) (or head loss, "h" (m)) and flow rate through pipes. Head loss can be calculated using the Darcy–Weisbach equation in which the Darcy friction factor "f" appears : This formula must not be confused with the Fanning equation, using the Fanning friction factor "f", equal to one fourth the Darcy-Weisbach friction factor "f": Pressure drop can then be evaluated as: or directly from where "ρ" is the density of the fluid, "V" is the average velocity in the pipe, "f" is the friction factor from the Moody chart, "L" is the length of the pipe and "D" is the