from the Howard Catalog

pg 306 this is wrong for a stock rocker and very wrong for the roller rocker shown
many other grinders are the same
for a much better analysis go to the B3RacingEngines.com and read the tech reports
VALVE TRAIN GEOMETRY Valve Train geometry is when the rocker arm tip moves from the intake side of the valve stem tip, across the center of the tip (at approximately mid lift), to the exhaust side of the valve stem tip (at full lift) and back.
After you have estimated the required pushrod length using a Pushrod Length Checker, use this guide to check for proper alignment.
1) The first step is to install a solid lifter and an adjustable pushrod. Mark the tip of the valve with a machinist dye or ink.
2) Install your rocker arm and set it up with zero lash.
3) Rotate the crankshaft clockwise several times. Take off the rocker arm.
The pattern of the rocker tip will be where the ink has been wiped away from the valve tip.
The pattern should be centered on the valve tip. If not, adjust the pushrod length to center the pattern