This depends on you simply registering with a name, password and e-mail address (for authentication purposes only). Then, when you are logged in, any saved changes that you make to any page are recorded in complete detail.
A printer friendly version of all pages can be obtained for your records.
Even if a page is changed 20 times you can still go back and compare your original copy with the current one. This is done by clicking on the history tab on any page and using the dot and circle indicators to compare versions.(For the technically minded this site is essentially a huge database and each saved copy is a fresh record).
In addition to this, if you go to your User:Yourname page (that you get allocated when you sign up) you will see a link to 'User contributions' in the left hand panel. This will take you to a listing of all the pages you have visited, the times you were there and, if you annotated the edit box by the save button, an account of the changes you made. A listing of up to the last 500 changes can be printed out as part of your academic record and can be used for Individual Performance Reviews (IPR) and Continuing Professional Development(CPD) reviews.