Field from previous record to new Form

[copernicus]

I have seen similar posts to mine, but I seem unable to grip exactly how to utilize some of the answers that I have seen. I have attached what it is I am trying to work with. I have a form that creates a record, this record contains multiple deposits as well as some other things. I need there to be a field which holds the total deposit balance from the previous record and puts it on the new form as 'Previous Balance'. Then a total deposit balance, which sums the previous balance as well as the deposits on the new form which have been entered by the user. I could probably do the second part if I understood how to have it get the previous value field populated in the table. Hopefully this makes sense, and I appreciate any assistance I can get.