A rating is a non-linear transformation that takes data from one to measurement to another. Most ratings convert river level to flow, but DataTamer treats ratings in a very general manner. Thus you can build a rating that acts as a calibration curve for a sensor that is either non-linear, or drifts, and this technique is used for turbidity sensors and PM10 instruments. DataTamer can apply two sets of ratings sequentially. For example, one rating set goes from river level to flow, and a second set goes from flow to sediment yield. The tree control in Manager or Hydro will show items for river level, flow, and sediment yield, and you just click on the one you want. The software will apply the ratings as required.
Ratings are stored as points in a table and the curve is computed using second order interpolation. This is slightly controversial as other countries use equations. The Ratings software lets you construct a curve based on calibration data, such as stream flow gaugings. The stage and flow are shown as points on a graph and you can fit a curve through the points. The editor lets you drag the rating points around to achieve the desired fit.
The software can accept cross section information. A gauging that includes bed level information across all the section can be used to compute both the area and the conveyance. The conveyance calculation gives the shape of the rating curve at the bottom of the rating curve, and the area information lets you see the velocities at the top end of the curve.
The screen shot shows a rating curve selected from part of the set. The top pane shows the river level with the gaugings plotted on top of the hydrograph. The lower four panes show the flow, cross sectional area and velocity plotted against river level. The grid control has the actual points in it. You start with this window layout and then change to full screen mode once you have selected a rating and gauging set. This just shows the rating curve and list of points. You can drag points around the curve using the mouse, or just type the numbers into the grid.