Remember dated exchange rates are not currently used in forecasting, currency fields in other objects, or currency fields in other types of reports. See this reference and vote this in IdeaExchange for Multi-Currency support for All Currency Fields .
Advanced currency management allows you to manage dated exchange rates within opportunities using Salesforce. Dated exchange rates allow you to map a conversion rate to a specific date range. For example, the exchange rate on January 1 was 1 USD to 1.39 AUD, but on February 1, it changed to 1 USD to 1.42 AUD. Your opportunities that closed between January 1 and February 1 use the first exchange rate (1 = 1.39), while opportunities that closed after February 1 used the second exchange rate (1 = 1.42).
Dated exchange rates are defined using a start date and a conversion rate. Each rate is in effect until either the end of time or the day before the next start date for that currency. The time between on start date and the next start date is called the exchange rate date range. These ranges can be as small as a day and as large as all of time.
Today we get a real scenario when dated exchange rates is not match with conversion rate.
This is screenshot from Opportunity report
and this from Forecast report
From screenshot above, opportunity report show USD 48.04, while from forecast report USD 48.02, this is not much different, but when the numbers getting bigger, the difference will be bigger.
Let us analyse:
This is screenshot from dated exchange rate
This is screenshot from conversion rate
Let's calculate this using Ms Excel
Reference: About Advanced Currency Management