Dietert Detroit Electric Permmeter (338) - Calibration

Hi guys,

Anyone here knows how to calibrate a Dietert Detroit Electric Permmeter? I have a problem in reading green sand permeability in my thesis, im having values greater than 500 in the 1.5D scale, also i really dont know if i read it correctly, if the permmeter is OFF the indicator points toward the maximum perm value, and the ZERO / minimum value is on the other side of the scale. help me please, thanky you very much. It is really hard when you do things on your own regarding instruments with no manuals no technician and no one to teach you but a single piece of paper.