1. Precipitation rate (PR) is the rate at which sprinkler heads apply water and should be consistent within a zone. Matching PRs requires using heads of the same type, manufacturer, and precipitation rate. 2. PR can be calculated using either the total area method by dividing total GPM by total area, or the individual head method using sprinkler spacing and pattern. 3. Reducing the radius of spray heads lowers the GPM according to manufacturer charts, but the GPM stays the same for rotors so the nozzle must be changed to match the new radius.