## Making a function call another function In this lesson, we'll learn about making a function call another function in Vyper. We'll use an example of a function that takes an amount of ETH in Wei and converts it to USD. First, we create a function to do the calculation. ```python def get_eth_to_usd_rate(eth_amount: uint256) -> uint256: """ Chris sent us 0.01 ETH for us to buy a coffee: Is that more or less than $5? """ eth_price: uint256 = staticcall(self.price_feed, latestAnswer()) * (10 ** 10) price_in_usd: uint256 = (convert(uint256, price) * eth_amount) // (1 * 10 ** 18) eth_amount_in_usd_uint256: uint256 = price_in_usd * eth_amount // (1 * 10 ** 18) return eth_amount_in_usd_uint256 # 18 0's, 18 decimal places ``` We can create an external function that runs our internal function. ```python @external @view def get_eth_to_usd_rate(eth_amount: uint256) -> uint256: return self._get_eth_to_usd_rate(eth_amount) ``` We'll say ETH amount uint256 returns a uint256. All we got to do is say return self.\_get_eth_to_usd_rate(eth_amount). This creates an external function `get_eth_to_usd_rate` that calls the internal function `_get_eth_to_usd_rate` passing the `eth_amount` as an argument. This is a useful technique when you need to expose an internal function. It allows you to keep internal functions private while still providing an external interface to access their functionality.