There are many YouTube videos showing this in use, but it suggests that it's automatic and following some fixture. It's not, but you can do a pretty good job just by paying attention. I've done rockers by hand on a grinding wheel with good results (shows no new pattern on the tappet or valve stem 5,000 miles later). Easier to hold the rocker straight to the abrasive by putting the shaft through it. The intake and exhaust rockers are different shapes but the pallets are the same.
Stop and examine the pallet under a strong lamp, tilt it slightly and rotate, and watch how the light passes across the curvature; if you see a line or ripple remove it. IMHO as long as you get this:
1. no flat spots
2. no edges
3. left to right surfaces an exact match
4. shiny!
it's probably good enough.
