### Fee Growth Outside Inside of Uniswap V3's code, there is a state variable called `fee growth outside`, and it's used to calculate both the `fee growth above` and `fee growth below`. In the next few videos, we'll explain how this works. In this video, we'll start by explaining how `fee growth outside` is initialized and how it's updated. Let's first start by defining some variables: `f_g` = Fee growth `f_o,i` = Fee growth outside at tick i Next, let's take a look at the algorithm. The state variable `fee growth outside` is initialized as follows: ```javascript f_o,i = f_g if i <= current tick i_c = 0 otherwise ``` This may not be obvious right away why `fee growth outside` is initialized in this way. However, in the next couple of videos, when we look at an example of how `fee growth outside` is used to calculate `fee growth above` and `fee growth below`, this will become more clear. The way that `fee growth outside` is updated is as follows: When `f_g` crosses tick i, ```javascript f_o,i = f_g - f_o,i ``` So that's how `fee growth outside` is initialized and updated. In the next couple of videos, we will see how this algorithm correctly calculates `fee growth above` and `fee growth below`.