Insulin Question

Patient: Dr. put me on Humulin N. 50 units and a slideing scale. I am confused. I think I take 50 units and then add more later according to a slideing scale? I think he said take 2 units for every 50 points above 150. Does that mean I take 50 units in the morning and thenso many extra that night. Say for instance 50 in the morning and if my sugar is 300 at night I take 8 more units?