how to generate automatically?

hi,
any one here know how to generate a number like document number automatically? tat means i do not want the user to key in after press the add button Access will generate a document number for that record.

any one can help me??
thanks a lot ...

Just add a field name called "Number" (or whatever you want it to call) in the table you're going to work with.. and then make that field a "Autonumber" and then add that field in the form you want the user to work on.. and then it will auto generate the number for you.. you can lock that field under "properties" (right clicking) so taht user can't change the number.

oic ..
now my case is i got a main form and a subform. the autonumber will be in the subform. so everytime the user add a record it will automatically add 1 according to the numbers of the records added.. that means 1 number for 1 record in the subform. and then everytime the form is reset the number will back to 1 again. is there any way to do so?