We recently added a new calibration target type in Groundwater Vistas called the flow direction target. This may be a bit confusing because we also have a gradient target. The latter is made up of a triangle of 3 head targets linked together to define the direction of flow at the centroid (and optionally the magnitude of the gradient). The flow direction target, on the other hand, is a point observation of flow direction. If you define a target in Vistas and pull down the list of target types at the top of the target dialog, you'll see "flow direction" way down the list. The target value in this case is the direction of flow. The direction is a mathematical angle so zero degrees is East, 90 degrees is north, etc.
The general idea behind the flow direction target is to match contaminant plume movement in a flow calibration. One of our users recently tried this by putting flow direction targets down the center-line of a plume and then using pilot points for hydraulic conductivity with Pest. The result was a very good match to the observed movement of the plume without having to calibrate the transport model along with the flow model.