auto increment values in text box

[psuplat]

hi.

how can i increment a value (number) in a text box placed in a form header every time i input a value into a field on form detail section?

in form header is text box "count"

in form detail is tex box "SN"

after i input value into "SN" i want to value in "count" to go up by 1

i guessing it has to be done if SN after update event but how i don't know

 

[missinglinq]

Is Count a bound control? Is the value being stored in a table or are you simply using it as a counter for the current session of Access?

Do you want Count incremented if SN already has a value and the user goes in and enters a new value in it, or only the first time it's populated?

 

[psuplat]

just a counter for the current session, it's not bound.
and i want to to increment only when it's being populated for the first time