If any changes in currency rate,the foreign exchange gain/loss will be operate.
-Customer issue an invoice amount USD100 at 01/01/2011. At that time the USD currency = 3.6 so the figure in RM 360.
-After a month (01/02/2011) customer make payment = USD100 for this invoice and the currency rate at 01/02/2011 = 3.8 So the figure in RM 380
When check journal,means that the amount gain RM20 and automatically posting to forex gain account.