I perhaps don't understand your question or perhaps you don't understand backlash.
Backlash is a the clearance between mating gear teeth and allows gear teeth to mesh without binding. There is a minimum desirable backlash for any given gearset since the backlash clearance also allows for a film of lubricating oil between the teeth.
Go to http://www.wmberg.com/catalog/pdf/b00k2-16.pdf
and download the PDF file. Backlash, as a function of gear quality is discussed starting on page 8.