Final answer:
When measuring backlash, one gear must be held in a fixed position while the other is rotated back and forth. This allows engineers to observe the relative movement between the gears and determine the amount of clearance or play between their teeth.
Step-by-step explanation:
In the context of mechanical engineering, when measuring backlash, one gear must be held in a fixed position while the other is rotated back and forth.
This is done to observe the relative movement between the two gears and determine the amount of clearance or play between their teeth. Measuring backlash is important in gear systems as excessive backlash can result in decreased efficiency and accuracy.