Quite frankly in VCE accounting the real truth is that you don't need double lines really anywhere! Especially in the exam, the will not take or award marks for simply drawing to parallel lines. Double lines is just a nice little 'convention' used in Accounting, and usually indicates a completion of a report or a ledger (have you learnt double entry yet- I'm assuming that your're doing 3/4 this year). However, for the sake of not loosing any marks (which, I think is pretty harsh especially in 1/2) on SACS if your instructor is really pedantic, just do it.... I also did out of habit when I did accounting last year. If anything, you should only have double lines at the end of the Balance Sheet, Income Statement and CFS (reports) and also when balancing/closing off an account in the general ledger.