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. So let's suppose we have a beaker. In that beaker we have a sample a mixture of different types of proteins as shown in the following diagram. Now, what we want to do is we want to use several of the different types of procedures that we spoke of earlier and basically purify our sample, purify and isolate some specific type of protein found inside that mixture.