So the purification level is equal to the ratio of the specific activity of that particular procedure to the specific activity of that original sample. And notice that it's also ratios the units cancel out and we don't have any units. And just like the original mixture is given a percent yield of 100 that original mixture is given a percent yield of one. And following our procedure, if that procedure actually worked and we purified our sample this quantity has to increase. So specific activity increases and purification level also increases if our procedure is actually working and the yield decreases because as we go from one process to another we usually lose a certain amount of product, a certain amount of protein in that procedure. So now, to see actually how these quantities can be used to basically determine if the purification procedure is working let's take a look at a hypothetical example.