(Open pressure - closed pressure) ÷ lift = spring rate in lbs. per inch. Lbs. per inch at the valve × rocker arm ratio = spring rate on the cam, tappet, pushrod, adjuster.
Example: 800 lbs. open - 300 lbs. closed = 500 lbs., ÷ .800" lift = 625 lbs. per inch deflection rate; with a 1.7:1 rocker arm the cam etc. sees 1,062.5 lbs. per inch.
Depressing the adjuster .010" requires 10.625 lbs. of pressure.