The premium/discount is calculated against an index price. The index price is calculated from spot exchange prices and are weighted as follows:
The difference between this script and other available scripts, is that exciting script seems to only focus on one exchange. This script is also open source.
Added the possibility to select the reference price. Choises are Bitmex Indices (as used in previous script) and Tradingviews index. Default is the TradingView index.
In true TradingView spirit, the author of this script has published it open-source, so traders can understand and verify it. Cheers to the author! You may use it for free, but reuse of this code in a publication is governed by House Rules. You can favorite it to use it on a chart.