
Spot Index Price
The Index Price is determined by Spot prices from 6 major exchanges (Huobi, OKX, Binance, Kucoin, Mexc, Gate). For example, BTC/USDT Index Price is the volumeweighted average price in USDT of BTC in 6 exchanges.
Calculation rules
1.1 If the spot price of an exchange deviates from the median of all exchanges by ±3%, the spot price data of this exchange will be excluded; however, if more than three exchanges return prices that deviate, the price will be considered as a valid price.
1.2 If the quotation data of an exchange is updated slowly for a long time or if the price deviates from the preset percentage, the spot price data of this exchange will be excluded.
1.3 If the data quality of the excluded exchange is restored, its original data weighting will be restored.
1.4 If only 3 or more exchanges are connected, exceeding the median ± 3% then the reference price will be calculated as median * (1.03 / 0.97) (backend can be matched);
1.5 if there are only 1 or 2 exchanges then directly weighted by the rules
Underwriting strategy
1.6 If the index price is calculated abnormally, or all sources are kicked out, then use the middle price of the handicap [(Bid1 + Ask1) / 2] as the index price.

Mark Price
In traditional futures, a position value is usually marked to the last trading price. However, unnecessary liquidation might occur if the market is manipulated or illiquid, and the Mark Price swings significantly from its Index Price.
The mark price for perpetual contracts is calculated using the funding fee basis rate:
Mark Price = MEDIAN (Mark Price1 , Mark Price2 , Latest Price)
Where
Funding fee basis ratio = funding fee rate at the previous settlement point * (time until the next funding fee payment / funding fee time interval)
Mark Price 1 = Index Price * (1 + Funding Fee Basis Ratio)
Mark Price 2 = Index Price + MA (30minute basis) ((Bid1 + Ask1)/ 2  Index Price)
MA (30minute basis) = Moving average ((Bid1 + Ask1) / 2  index price)