It is the original and most popular scoring system. It uses all three reports to generate a score using Fair Isaac's calculator. Fair Isaac tells everyone the % each category is based on, but the calculations are a secret. Other companies now have their own scoring system, but none are the same. I've used Truecredit, Experian Plus, and FICO. All three have almost a 50 point difference.

Go to myfico.com and it has info on what it's all about.