Contour line future weather patterns. Isobars are commonly used in television weather reporting. Isallobars are lines joining points of equal pressure change during a specific time interval. These can be divided into "anallobars", lines joining points of equal pressure increase during a specific time interval, and "katallobars", lines joining points of equal pressure decrease. In general, weather systems move along an axis joining high and low isallobaric centers. Isallobaric gradients are important components of the wind as they increase or decrease the geostrophic wind. An isopycnal is a line of constant density. An "isoheight" or "isohypse" is a line of constant geopotential
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