# Time indicators

We define TD as the total period of time during which the demand discharge is non-zero and TEF as the total period of time during which the effective discharge is non-zero. We introduce the indicator IND4 = TEF/TD. It compares the duration of delivery of the effective volume with that of the demand volume. This indicator is dimensionless and can only be calculated for individual offtakes since it doesn’t have any significance for all the offtakes taken together.

We also define two time lags: DT1 and DT2. DT1 is the time separating the start of the water demand and the start of the effective discharge. This time is positive if the effective discharge arrives after the demand discharge (Cf. figure 30). DT2 is the time lag between the centers of gravity of the demand hydrograph and the effective delivery hydrograph.

__Figure 30__

All these indicators are defined for each offtake. They can be calculated for any particular period of the simulation that the user wants to focus on.