An overlay represents the degree of difference between a selected rating and another rating that you have specified under overlay reference. It’s a comparison between two ratings.

Let’s say you had selected the GTX rated odds and were referencing them against the Morning Line odds. If the GTX odds were 2.0 and the Morning Line (ML) odds were 4.0, then an overlay situation exists. If the figures were reversed, it would be regarded as an underlay.

Before you use the Overlay option in the System Developer, there are several settings in GTX that need to be attended to.

To continue the above GTX/ML example, the first thing you need to do is to select, on the menu bar: Setup>Ratings (Extended)

In the Setup Rating box that opens, click on the GTX button, then:

Set the Market Parameters>overlay ref to Morning Line.

Click OK

Then, from the menu bar, select Setup>Ratings.

In the Rating Display Options box, in the Overlays section at bottom left, we suggest that the absolute price ratios option is selected because it’s a bit easier to understand than Probability % difference.

Given that you may want to visually check the two sets of odds in the Field View, it would be a good idea to make sure in the Rating Display Options box that the GTX and Morning Line odds are both displayed similarly, for example both displayed as Decimal Odds, at least temporarily, until you satisfy yourself that the process is working as you envisaged.

GTX calculates using decimal odds, no matter how you have the odds display settings in this box – these display settings govern only how the odds are displayed in GTX, not how they are calculated. Also bear in mind that the comparison of the two sets of odds may not appear to be exact – GTX calculates to two decimal places, but the result is rounded to one decimal place for display.

You would also need to display the Morning Line Odds column and Generic Price (or GTX Price) column side by side on the Field View, and if using Generic Price you would need have the field ranked by GTX so that the 'Generic Price' will be the GTX prices. (Please note that the ‘Generic Price’ column displays the odds as calculated by whatever rating method the field is currently ranked by. For example, change the field ranking from GTX to Trakform and the values in the ‘Generic Price’ column will change from GTX prices to Trakform prices).

To check how it works, first load an historical race meeting (with results included) to the Field View. If you have changed any of the Market Parameter settings, i.e. ‘overlay ref’, ‘market percentage’, ‘distribution’ or ‘absolute price ratios’, you will need to do the following:

On the menu bar, click Race>Synchronize/Re-Calculate and in the box that opens, select synchronize only and loaded races and click the Synch button, then Close when it's done.

Then open the System Developer, or if it was open during the setting changes, close it and reopen it. Select an empty system.

On the Rating tab, select GTX>Overlay. Then click the Analyze by button (above the system rules text box) so that it shows GTX Overlay in the text field beside it.

Then run the system over loaded races. As you have not yet entered any rules in the system to limit selections, all horses in the loaded meeting/s will appear in the result.

In the Selections pane, you will see all the horses in the loaded meetings, and you will see the overlay value in the Parameter column at right. In simple terms values greater than 1 indicate overlays and values less than 1 indicate underlays.

You can then choose one of the selections, note its overlay value, then check that horse’s two odds columns in the Field View to check if you are getting the values you expect.

Once you decide to use an overlay rule in a system and also determine a Min/Max values as a starting point and enter against that rule, then run the system over historical data for a selected date range.

First you need to again select Race>Synchronize/Re-Calculate on the menu bar, then select synchronize only, enter the date range of your historical data, then click the Synch button, then Close when it's done.

You don’t need to ‘synchronize’ every time you run a system. When it’s done, it’s done. You would need to do it again only if you change any of the settings.