1. What is the methodology to calculate the mark price (or reference price)?

The mark price will be calculated as below:

For Spot

If there are price oracles setup for the pairs then the mark price will be the ratio of the two prices coming out from the price oracles;

Otherwise, the mark price will be the volume-weighted price of the most recent 15 transactions or its initial price set by the creator of the pair.

For Option

Mark price will be derived using Black Scholes formula with an on-chain volatility surface. On-chain volatility surface will be updated periodically by referencing and aggregating from external sources