Think Backwards with Sweeps
Many years ago (actually 25 years, pre-Quicken), my wife was balancing our checkbook when the battery died in her calculator. She came into my home office and asked to borrow mine, I happily lent it to her.
As I expected, she was back a few minutes later with some choice words for me. I lent her my HP 15-C, a calculator that relies on reverse polish notation. If you are not familar with RPN, you essentially enter the numbers first and then the operation: 3+4= is typed in as 3 4 +. For balancing a checkbook every time you type a number and then click the add button you have the next value for your register.