automated fields in a receipt

[eyalco via AccessMonster.com]

I have a receipt form (access 2003) where I write checks received (between 12
- 36 checks for each client).

My question is : how do I automate check numbers (it's a running number by
order), same bank (all checks are from 1 bank : how do I make each line in
the receipt writing the same bank automatically) etc'.

I placed the following in the default value properties: "DMax
"CheckNumberFieldHere", "tableNameHere")+1"
and it's ok but when I go to the next row, the check number goes 0 but
there's another row with the following needed number (it actually creates 2
new rows : 1 =0 and the 2nd=the needed number). The following desired number
skips a line.

Can you please figure this one out?

Thanks.