Every save writes lines that sum to zero, dated to the period.

Purchase 800 rent paid: debit Rent 800, credit main bank 800. Paid 100 of 300: debit Expense 300, credit cash 100, credit vendor 200.

Sale 1000, collected 600: debit cash 600, debit customer 400, credit Revenue 1000.

Payments only settles: collect 400 = debit cash, credit customer. Owner puts in = debit cash, credit equity. Owner takes out = reverse.

Timing: spread expense parks in Prepayments and releases 1/n monthly. Spread sale parks in Unearned revenue. Fixed assets depreciate monthly. Later months never rewrite old cash.

Balance check posts target minus previous per cash account, then a single Misc line for the unexplained net change. Unchanged posts nothing. That residual is where small skipped spending lives, which is why Home profit reads as locked.