Theory of Machine
The contact ratio is given by

(Length of the arc of approach)/cosφ
(Length of the arc of contact)/(Circular pitch)
(Length of path of recess)/(Circular pitch)
(Length of the path of approach)/(Circular pitch)

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Theory of Machine
In a mechanism, the fixed instantaneous centers are those centers which

Remain in the same place for all configurations of the mechanism
None of the listed here
Vary with the configuration of the mechanism
Moves as the mechanism moves, but joints are of permanent nature

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