Quality gears are capable of transmitting substantial tooth loads with remarkable smoothness, having variations in motion of only a few microns at the pitch line. These loads though, can be large enough to produce tooth and other deflections of tens of microns. The few microns of variation in transmitted motion can only be achieved by compensating in some way for these deflections.
That way is by means of Profile and Lead Corrections

Tooth stiffness
Tooth loading
Transmission error
Long correction
Short correction
Specification
Thermal effect
Manufacturing considerations
Measurement of the profile
Sample calculations

As well as many of the above:
Shaft bending
Tortional deflection
Alignment errors
K Charts
Sample calculations

Plus much, much more
All the Formulas
Lots of Diagrams
Superb Printout for producing your own manual
PDF format allows use on any system

Download a PDF of the
Contents pages of Profile Correction and Lead Correction