leakdown tester, how 2?

Greetings,

I bought a leakdown tester at Harbor Freight, which may be the problem :-)

I have read and understand the process, but never done it, until now. Got my compressor set at 80psi, attach it up, set the engine to TDC on the compression stroke for number one, and attached the tester to the cylinder.

What happens is, that the directions tell me to open the pressure valve until the leakdown gauge reaches 0, or the position marked as SET.

When I open the valve, the leakdown gauge goes around to the top of the settings, at 0, but the input gauge, is only reaching

20psi........ If I open the input to the full 80psi, the leakdown gauge wraps around way past the 0 point, and pins all the way up high, making it useless.

Should there be away to calibrate the leakdown gauge? I am just not sure if I am missing something that is required, as at 20psi, there is no leaking of consequence, and for me to set the leakdown to 0, seems an odd thing to do.

I would have thought I should set the input to 80psi, and the leakdown percentage would read on the leakdown gauge.....

If anyone has done this, seen it, or wants to take a guess, I am up for all the help I can get.

Thanks in advance.

John