The equation above can be used to plot the Fanno line, which represents a locus of states for given Fanno flow conditions on an "H"-"ΔS" diagram. In the diagram, the Fanno line reaches maximum entropy at "H" = 0.833 and the flow is choked. According to the Second law of thermodynamics, entropy must always increase for Fanno flow. This means that a subsonic flow entering a duct with friction will have an increase in its Mach number until the flow is choked. Conversely, the Mach number of a supersonic flow will decrease until the flow is choked. Each point on the Fanno line corresponds with a different Mach number, and the movement to choked flow is shown in the diagram.