Suppose that a voting facility processes an average of $50$ people per hour $($throughput R $=50)$ and that, on average, it takes $12$ minutes for each person to complete the voting process $($Flow time T $=12$ minutes$/60$ minutes$/$hour $=0\mathrm{.}2).$ In the graph we can see that WIP $=50*0\mathrm{.}2=10\mathrm{.}0,$ so we would expect to find about $10$ voters inside the facility.

You may move the sliders to change R and T to produce other values of WIP. Note that, in this graph, changing Throughput R changes the slope of the line and that changing Flow time T changes the location on the line.