Here's the Tas Tab form guide:
http://www.tastab.com.au/racebet/fo...num/default.asp
And here's the Unitab website:
http://www.tabonline.com.au/

On the Tas Tab form guide, click on a horse's name and it'll give you a complete form rundown for that horse including a rating for each run. The rating will be in the form of a number like 645 or 725 or something. To convert them to weight ratings, I simply slip a decimal point in there and make it 64.5 or 72.5. Technically speaking, doing that is probably not 100% accurate, but it's worked out okay for me. So, I get the two ratings I want and then average them out. In that instance, it would be 68.5.

Next, I add the horse's Unitab rating. These ratings are a score out of 100 on the right side of the screen beside each runner. Before using it in my ratings, I divide it by 2 though so it's a score out of 50 instead of out of 100. So, if the horse has a Unitab rtg of 93, I turn that into 46.5 and add that to the rating I have from the Tas Tab site. Then I add small bonuses and penalties depending on the days since last start, the jockey, the barrier and the state of the track. Once I've done that, I'll have a total from which I subtract the horse's handicap weight and what's left is the horse's rating for today's race.