To figure that out, let's look at an actual z-table. We want 99% confidence. Another way to think about it, if we want 99% confidence, if we just look at the upper half right over here, that orange area should be 0.475, because if this is 0.475, then this other part is going to be 0.475. We want to get to 99%, so it's not going to be 0.475. We're going to have to go to 0.495 if we want 99% confidence. This area has to be 0.495 over here, because if that is, that over here will also be, so that their sum will be 99% of the area. This is 0.495, this value on the z-table right here will have to be 0.5, because all of this area, if you include all of this, is going to be 0.5.