We have the specific activity. We also have yield and purification level. So let's begin by discussing what these quantities actually mean and then let's take a look at an example at how we can purify proteins and use these quantities to basically determine whether or not our technique is working. So let's begin with the total protein. The total protein is simply the total amount of protein that we begin with in our sample before we carry out that particular purification technique. And this is usually given in milligrams.