Using Dmax for more than 2 fields

please help
i have this fields in the form and table:
hiredate , serial,department
i have a command bottom with save option
i want to do this
when i save the current record in the form which is named as Emp
so that to do the following with the save bottom
To sort the current record by hiredate and put serial for the emp i mean
that when i save the record the code looks for the hiredate for this employee
and create a serial for him
i have used this code and it makes serial as well
serial = Nz(DMax("serial", "emp"), 0) + 1
but i need to sort the serial by hiredate
for example
emp has been hired in 1/1/2000
and other is hired in 20/1 2000
so what i need is to do this
when i click on save bottom :
the text named serial to see which emp is before the other in hireddate than
it serial him as number 1for example
and the other as number 2 or higher number
i wish that i have explained my request
So:
please help me