Gemini uses an index provided by crypto index calculator Kaiko in order to determine an independent market price of crypto assets based on other platforms. The index is used to add stability to the Gemini Mark Price. 

The Mark Price is based on the Median (Best Bid, Best Ask, Last Trade) and then bound by the Index. This bound is currently set at +/-0.05%. The bound prevents the Mark Price from being moved too far away from the common market price, ensuring that accounts are not impacted by peaks and troughs in the Gemini price that are not reflected on platforms elsewhere.