Which of the following is NOT a requirement for vacuum gauges on vehicles?

The correct answer is high-cost construction materials, as this is not a requirement for vacuum gauges on vehicles. The primary focus regarding vacuum gauges is on their functionality, ease of use, and reliability rather than the cost of materials used in their construction.

For a vacuum gauge to be practical for drivers, it must be visible and legible at all times while operating a vehicle, ensuring that crucial information can be readily monitored without distraction or difficulty. Additionally, reliable construction is essential to guarantee the accuracy and durability of the gauge under varying conditions. These factors are vital for maintaining the vehicle's performance and ensuring safety on the road. High-cost materials do not inherently correlate with effectiveness or reliability in the function of vacuum gauges.