Work measurement terminology: what is “performance rating” mathematically? In time study, performance rating relates the observed worker pace to the defined normal performance. Which expression best represents the performance rating factor?

Introduction / Context:
Time study establishes standard time using observed time, performance rating, and allowances. Correctly defining the performance rating is critical because any error scales the computed normal time directly.

Given Data / Assumptions:

• Observed performance is the analyst’s assessment of worker pace relative to “normal”.
• Normal performance equals 100% (or 1.0) on the defined scale.
• Rating factor is typically applied multiplicatively to observed time.

Concept / Approach:
Performance rating (RF) is the ratio of the observed pace to the defined normal pace. If a worker operates at 120% speed relative to normal, RF = 1.20. Normal time = observed time * RF. None of the provided arithmetic forms (sum, difference, or product of two absolute performances) are correct statements of RF by themselves.

Step-by-Step Solution:
Define rating: RF = observed performance / normal performance.Apply to time: normal time = observed time * RF.Since options A–C are incorrect formulations, select “none of the above”.

Verification / Alternative check:
Many organizations use Westinghouse or synthetic rating aids, but the underlying mathematics remains a ratio against the normal benchmark.

Why Other Options Are Wrong:
(A) and (B) imply dimensional addition/subtraction of two performances; (C) multiplies absolute values rather than creating a ratio; none match the standard definition.

Common Pitfalls:
Confusing “rating” with “allowance”; using percentage points incorrectly; forgetting to convert percentages to multipliers.

Final Answer:
none of the above