In this case, the moles of NADH produced per the time that we're basically studying. So the time can be a minute, it can be five minutes and so forth. So the enzyme activity is the moles of product divided by the time. Now, once we know the enzyme activity, we can then calculate what our concentration of that protein is and once we know what the enzyme activity and the concentration of that protein, that enzyme, in this case lactate dehydrogenase we can then calculate the specific activity, because the specific activity is the ratio of the enzyme activity to the concentration of that protein. So enzyme activity divided by amount of enzyme. So what exactly is this value?