MasterChef accSushiPerShare

Hi guys, I was just reviewing MasterChef contract from SushiSwap and had this question.

Here is the contract

In the lot of places they do multiplication and division by 1e12, but couldn't understand why. Couldn't even understand the concept of accSushiPerShare variable

For example in the updatePool function

pool.accSushiPerShare = pool.accSushiPerShare.add(