Contour line positioned at a contour line (when they are, this indicates a measurement precisely equal to the value of the contour). Instead, lines are drawn to best approximate the locations of exact values, based on the scattered information points available. Meteorological contour maps may present collected data such as actual air pressure at a given time, or generalized data such as average pressure over a period of time, or forecast data such as predicted air pressure at some point in the future Thermodynamic diagrams use multiple overlapping contour sets (including isobars and isotherms) to present a picture of the major thermodynamic
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