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# An approach to creating a synthetic UMA token (perpetual), the price of which is tied to the index value
It is supposed to create synthetic tokens (perpetual), the price of which is tied to the values of various indexes.
Examples of possible indexes:
- **SPAC-5** - An index that includes the shares of the 5 most active SPAC according to [Yahoo.Finance](https://finance.yahoo.com/u/yahoo-finance/watchlists/most-active-spacs)
- **SPAC-FinTech** - An index that includes shares of [SPACs aimed at FinTech companies](https://spactrack.net/activespacs/).
A feature of such indexes is the periodic revision of the basket of stocks included in the index.
This is associated with some difficulties in price feed implementation. To overcome these difficulties, it is proposed to use the following scheme:
1) The formula for calculating the index:
* N – number of shares;
* Qi – quote of share i;
* K – Correction factor, used to smooth the index values when the basket is changed;