# How It Works

## Prior Work

See <https://docs.chain.link/data-feeds/api-reference#aggregatorv3interface> for documentation on the Chainlink Oracle interface.

## Supported Frax Assets

Currently frxEth/ETH and sfrxEth/ETH are supported.

## Frax Dual Oracle Price Logic

### frxEth

The frxEth price is determined from two onchain price sources. The first price source is the frxEth / ETH Curve pool EMA Oracle - [0xa1f8a6807c402e4a15ef4eba36528a3fed24e577](https://etherscan.io/address/0xa1f8a6807c402e4a15ef4eba36528a3fed24e577). This price is bounded to be 0.7 at the lowest (0.7 frxEth = 1 ETH) and 1 at the highest (1 frxEth = 1 ETH).

The second price source comes from the Uniswap frxEth / FRAX pool TWAP oracle - [0x36C060Cc4b088c830a561E959A679A58205D3F56](https://etherscan.io/address/0x36C060Cc4b088c830a561E959A679A58205D3F56). We then retrieve the price of ETH in USD from this chainlink oracle ([0x5f4eC3Df9cbd43714FE2740f5E3616155c5b8419](https://etherscan.io/address/0x5f4eC3Df9cbd43714FE2740f5E3616155c5b8419)) and the price of FRAX in USD from this chainlink oracle ([0xB9E1E3A9feFf48998E45Fa90847ed4D467E8BcfD](https://etherscan.io/address/0xB9E1E3A9feFf48998E45Fa90847ed4D467E8BcfD)). These chainlink prices are used to convert the frxEth / FRAX pool price into a frxEth / ETH price using the following equation:

```
ethPerFrxEth = (fraxPerFrxEthUniswapTwap * usdPerFraxChainlink) / usdPerEthChainlink;
```

This price from Uniswap is similarly bounded between 0.7 and 1, mirroring the Curve price.\
\
The lower of these prices is returned as priceLow and the higher is returned as priceHigh. These prices are then written to the frxEth / ETH Frax Oracle.

### sfrxEth

Simply retrieves the pricePerShare() from the sfrxEth contract, retrieves the priceHigh and priceLow in the same manner as the frxEth Dual Oracle outlined above, and returns the following equation:

<pre><code><strong>priceLow =  (SFRXETH_ERC4626.pricePerShare() * frxEthEthPriceLow) / 1e18;
</strong>priceHigh = (SFRXETH_ERC4626.pricePerShare() * frxEthEthPriceHigh) / 1e18;
</code></pre>

This works because pricePerShare() returns how many frxEth a single sfrxEth is worth. pricePerShare() goes up over time.

These prices are then written to the sfrxEth / ETH Frax Oracle.

## How to use with Chainlink Interface - AggregatorV3Interface

Simply call <https://docs.chain.link/data-feeds/api-reference#getrounddata> or <https://docs.chain.link/data-feeds/api-reference#latestrounddata> on the Frax Oracle contract for the asset you want the price of.

## Frax Oracle on L2

Coming soon<br>


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