I am not in four unit...yet, but i have found some good tutorials on Senior Mathematics (2U, 3U and 4U). I included 2U and 3U because i found some good websites that are good for revision if your to lazy to pick up the textbook and work lol.
This is a good calculus revision site, it has limits, and mainly differential calculus, good revision of the year 11 work, very simple yet handy explainations.