Figure 21. Graph of Timing Equation. The y axis is T, time in seconds and the x axis is D, distance in feet. The "Acceptable" range is above a line on the graph indicated as follows: If D = 5 to 8 feet, then T = 5 seconds. If D = 8 to 18 feet, T increases at approximately 1:1 with the end of the line at D = 18 feet and T = 12 seconds. The maximum value shown for T is 13 seconds and for D is 18 feet. Values below the line on the graph are indicated as "Unacceptable."