If one stall has two fixtures that cannot be operated simultaneously (e.g., a showerhead and a handheld wand where only one can be operated at one time), the flow rate for the purposes of the credit should be the higher of the two. If one stall has two fixtures that can be operated simultaneously (e.g., dual showerheads that can both be operated at the same time), the flowrate for the stall is the sum of both fixtures.
Updated 10/1/13 for rating system applicability.