The opening float balance equals the closing float balance from the previous batch.
The closing float balance equals the opening float balance plus the net batch gain/advances minus the float firm transactions.
In the example below the opening balance is $48,429.95 plus $1,352.00 (being the net gain) less the float transaction $29,955.75. This gives us a closing total of $19,826.20
When the batch is updated the closing float balance is updated. The float balance is not considered current until the batch has been updated.