Most modern sprinkler timers have a feature that lets you use a Watering Index – it is often called a "Seasonal Adjust" or "Water Budget" feature. The Watering Index (%) modifies your sprinkler controller's watering runtimes. It does this by controlling the watering runtimes for all electric valves managed by your sprinkler controller. By adjusting the Watering Index on your sprinkler controller, all your watering runtimes are either increased or decreased. The adjustment is effectively a percentage (%) of the maximum watering runtime allowed by the sprinkler controller for each valve. As an example, if you water for 6 minutes in summer (at a 100% Watering Index), a 50% Watering Index setting would reduce sprinkler runtimes to 3 minutes.