Final answer:
The highest end of the scale for mechanical gauges used to measure test pressures must not be greater than 2 times the test pressure.
Step-by-step explanation:
The highest end of the scale for mechanical gauges used to measure test pressures must not be greater than 2 times the test pressure. To understand why, let's consider an example. Suppose the test pressure is 10 psi. If the highest end of the scale is 20 psi or higher, it means the gauge can measure pressures beyond the actual test pressure, which would not be accurate.