Using Filemaker Pro 10 on A Mac PPC using system OS X 10.5.8
The records are layed out as follows:
Xact Date, Basic Mortgage, Trans Amount, Previous Principal Balance, Insur Escrow, Tax Escrow, Total Escrow, Principal Paid, Interest Paid, New Principal Balance, Comment, and there are running Summaries on Total Escrow, Principal Paid, and Interest Paid.
Basic Mortgage is an auto-entered field and Total Escrow is a calculated field.
The Previous Principal Balance uses GetNthRecord to reach back to the previous record and get the New Principal Balance from that record. If (Get ( RecordNumber ) - 1 = 0; 0; GetNthRecord ( NewPrncplBlnce; Get ( RecordNumber) -1))
The Previous Balance field of the current record will be dated until the current record is closed AND the New Principal Balance of the current record is updated with a New Balance.
It gets worse but let's go slowly.