Now, what does the specific activity actually tell us? Well, it tells us how pure or by how much more pure our sample is following that purification technique. And usually if the technique actually works this specific activity value has to increase as we'll see in just a moment. Now, let's move on to our yield. So the yield or the percent yield basically tells us how much of that protein that we essentially want to isolate we have left over compared to how much we begin with. So this describes the enzyme activity that is retained following each purification step and it is given as a percentage.