Calibration - the process of refining the model representation of the hydrogeologic framework, hydraulic properties, and boundary conditions to achieve a desired degree of correspondence between the model simulations and observations of the groundwater-flow system, which includes both measured hydraulic-head and flux.

Calibration Target - measured, observed, calculated, or estimated hydraulic-heads or groundwaterflow rates that a model must reproduce, at least approximately, to be considered calibrated

Steady-state simulated head distribution, near Kalamazoo, Michigan, U.S.A.

Comparison of simulated head vs. observed Static Water Levels (SWLs). (SWLs are measured water levels at the time of well installation, before pumping). The red 45 degree line is the line of perfect agreement - points falling on the line are an exact match. Note that the "data cloud" is centered on the line of perfect agreement. The noise (spread of the data cloud) is due to uncertainties in well location and elevations, as well as spatial and temporal varaibilities not captured by the simlation.