add fields and variables

[Revenant]

Zubrag, great job, this script is great, and I really appreciate you keeping it stp (short and to the point), and free. 

Please feel free to let me know if my suggestion is impossible.

I want to add new fields, and have the administration page automatically calculate the differences between them.  For example:

User enters 100 into field x, and 103 into field y, then the administration totals the difference by subtraction is 3 for that user.  If it wouldn't be a hassle, I would love adding a new row that shows the total of all the users would come to.

Yours Sincerely,
Ivan

[Revenant]

Also, this has probably already been answered but how do I let the user update his own account information?