Machine Design
The contact ratio is the ratio of

Length of arc of approach to the circular pitch
Length of arc of recess to the circular pitch
Length of path of contact to the circular pitch
Length of arc of contact to the circular pitch

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Machine Design
In worm, gears, pitch lead angle is

None of these
The angle between the tangent to the pitch helix and the plane of rotation
Half the angle between two inclined faces in axial plane
The angle between the tangent to the pitch helix and an element of the cylinder

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