As you are relying on agents with a book of 20 receipts
what you could do is use some VBA to allocate/reserve 20 receipts at the time of issue
how you do that depends on you
you could store the magic number somewhere (eg in a config tabel or similar)
you could store the fact that you have issued a recipt block to someone, andpull that value + 20 as the next block available
you could write 20 blank receipts in a table.
you could put some code behind the form that records receipts and use that to trigger whatever warning / actions you need
you cannot rely on autonumber for this
to find out when all 20 receipts have been used, then you need to place some code behind the mechanism which records when a receipt is used and possibly issues another receipt book to that agent.
doing all this in one table is I suspect meaningless. you could work out when a receipt book is exhausted when mod(receiptno,20) = 0, which relies on the modulus function.
not understanding your table design or business requirement its hard to go further
What is your primary key?
be careful about using spaces in column names (it can cause problems later)
be careful about using reserved words as column or table names as this will cause problem later
presumably numbers is the cash amount and currency is the currency code, or is numbers the quantity of something and currency the cash value (assuming this is a single currency transaction system)
My honest advice would be to revsit your table design
what I think you have is at least two tables
one for agents
one for payments (identified by the receipt no)
the PK for agent probably should be an autonumber (but could be one of those compound elements so favoured by accounting software. often these comprise 4 or 6 letters of the name and 2,3 or 4 digits to make the value unique
Kallukallu could be Kalluk0072, assuming there were 71 other agents with the name prefix Kalluk
the pk of the recipts table should be the receipt number.
there shoudl be a FK from the receipts table to the agent table.
you coudl if you wished allcoate a block of receipts (with zero values) if you wished.
I'd rather be riding on the Tiger 800 or the Norton