It looks to me like they are basing the exchange value on the moving BTC-USD price and the current BTC to ZRC exchange rate. I just looked quick and it gave me a price of $1000=4548 ZRC. Roughly speaking $1000= 4.66 BTC atm so with a price of 1 BTC=1010 ZRC (pulled from their website) which gave me 4700 ZRC =4.66 BTC. I dont know where they pull the market rates but seems to be moving based on changing prices.