from old mag article
here is the procedure I hav 2 articles complete from the 70's I can post if wanted.
Connect the tester's regulator input to a compressed air source having at least 100 psi pressure. Slowly turn the regulator control clockwise until the tester's gauge registers 100 psi. Now connect the tester's female disconnect to the hose attached to the engine. The gauge reading will drop suddenly, then rise as the compressed air fills the cylinder. It will not, however return to 100 psi. Subtracting the gauge reading from 100 indicates the "percentage of leakage." (For example, a reading of 96 equates to a 4 per cent leakage; 100-96=4.) Disconnecting the hose from the tester's female fitting will release a jet of air from the hose and restore the gauge to its 100 psi setting. Test each successive cylinder by removing its spark plug and bringing the piston to TDC.