Well, the purification level is calculated by using the specific activity. So these two quantities tell us the same exact thing. So this is a measure of how effective each step is in purifying that protein that we want to isolate and study. 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.