Exchange rate
From Tardis Wiki, the free Doctor Who reference
An exchange rate was the rate at which one currency was be exchanged for another. In the Twelve Galaxies, one krin was equal to 200 kavlons, 90 forvalars, or 4,000 trynties. The Thirteenth Doctor, who was not familiar with any of these currencies, noted that she was "a bit behind on [her] exchange rates." (TV: The Ghost Monument)
