Final answer:
The maximum allowable variation in riser height or tread depth in a stairway system is 3/8 inch or 9.5 mm.
Step-by-step explanation:
In a stairway system, the variations in riser height or tread depth should not exceed a specific limit. The maximum allowable variation is 3/8 inch or 9.5 mm.
This means that the difference in height or depth between any two steps should not be more than 3/8 inch or 9.5 mm. This ensures uniformity and safety in the stairs.