How deposits work in TCR

The way deposits currently work in TCR is there are 2 fields on Job to store this information. One is Deposit Amount, which can be seen on Job screen. The other is Deposit Balance (hidden), which is set to Deposit Amount at first. Every time an invoice is generated for the job, system looks at Deposit Balance (not Deposit Amount) and deducts this amount from the total and reduces the balance by that amount.