Double Flank gear testing is considered a composite testing approach to gear measurement. It measures the “composite” of Index, Helix (lead), Profile and Runout errors in a gear.
Double flank testing consists of rolling two gears together in tight mesh (preloaded one against another without backlash) and measuring the center distance deviation as the parts rotate 360°. One of the gears in mesh is a master gear with very small elementals errors and the other is the component to be tested. After rotating for 360°, a chart is created showing the center distance variation between the two gears.