Sum up amounts which are unchecked
I have made a table with my credit card payments. I transfer money from my checking account to my cc account once a month. The amount I pay is the amount of the total of the payments of that particular month. To know which amount still have to be payed I added a button to my table which is checked as soon as the amount of the payment has been transferred from checking account to my credit card. So if I am planning on doing a new payment I have to add up the unchecked amounts. Now this last bit I want Filemaker to do for me. I want a field somewhere in a (separate table?) which adds up the unchecked amounts from my table.
So I imagine constructing a form which show only the unchecked amounts and adds them. But I really don't have a clue how I can make such a form, table or field. Obviously I can search for unchecked records within Filemaker but how can I make Filemaker to sum up all corresponding amounts?
Can anyone point me into the right direction?
Any help is really appreciated.