Liquid Template Variables - exchange rate
From Spiffy Stores Knowledge Base
If your theme has enabled currency support, then the user may choose to display all prices in their local currency, rather than in the store's local currency.
This currency support is enabled if a cookie spiffy_currency is created in the user's browser containing the 3-character currency code that the user wants to use.
If this cookie is detected, then a Liquid variable, exchange_rate is available which contains the current exchange rate between the user's display currency and the store's local currency.
If no custom display currency is active, then the exchange_rate will be equal to 1.