I use the Wizard Form Guides class indicator (Cls) eg. eq or dn and; the field strength (FS) as a guide. The FS "measures the difference between the quality of the field against which the horse raced last start and will confront in the forethcoming race." eg FS -2.0 means the upcoming race is 2.0 kg weaker for that horse than last start.

In combination with the Wrat and Impact Form, I have found it a good way to narrow down the chances.