Advanced Currency Management and dated exchange rates
Key Takeaway
Advanced Currency Management (ACM) converts opportunity amounts at the rate that was in effect for the opportunity's date, not today's rate.
Advanced Currency Management (ACM) lets an org that uses multiple currencies tie exchange rates to date ranges. Without ACM, Salesforce uses one static conversion rate per currency, and changing that rate re-converts every amount, including closed opportunities.
Static conversion rates without ACM
Without ACM, a multi-currency org uses static conversion rates. When you change a static conversion rate, amounts update using the new rate and Salesforce doesn't store previous rates. This means the converted value of closed opportunities changes too.