http://www.alaniztechnologies.com/headterms.html

Look under the MULTI-ANGLE VALVE JOB section. I'll cut it in here.

A multi angle valve job is the cutting or grinding of 2 or more angles on the seat and valve. The purpose of a multi angle valve job is to improve airflow. By now you have probably heard of 5 angle and radius valve jobs. The truth…… this is more applicable in the American iron heads. There just isn’t enough material in the small diameter seats or valves to see any real noticeable differences on a flow bench. A .5% gain maybe seen on a flowbench but the flowbench has a plus or minus error factor that has to be eliminated before a true flow figure can be attained. Older American iron heads may benefit from a five angle or radius valve job but only because the head is so bad to begin with. The Honda head is diffrent. Our flowbench testing has proven time after time that the correct angles and angle widths is what’s important. More CFM gains have been made through this procedure than applying 5 angles or radiuses.