1. **Problem Statement:** A technician is testing the exhaust emissions of a car running smoothly but with poor gas mileage. The technician uses two gauges: one for Hydrocarbon (HC) levels ranging from 0 to 2000 units, and one for Carbon Monoxide (CO) levels ranging from 0 to 10 units. 2. **Understanding the Gauges:** - The Hydrocarbon gauge is semi-circular with labeled intervals at 0, 100, 200, 300, 400, 500, 800, 1200, 1600, and 2000. - The Carbon Monoxide gauge is semi-circular with intervals from 0 to 10, with minor ticks at 0.5 increments up to 2.5. - The black button indicates which scale to read. 3. **Interpreting the Readings:** - The technician should press the black button to select the correct scale. - Read the needle position on the selected gauge to determine the emission level. 4. **Formula and Rules:** - No explicit formula is given, but understanding the scale and reading the needle position accurately is crucial. - Hydrocarbon levels indicate unburned fuel; high values suggest inefficient combustion. - Carbon Monoxide levels indicate incomplete combustion; high values suggest poor air-fuel mixture. 5. **Conclusion:** - The technician uses the black button to select the gauge scale. - Reads the emission levels from the appropriate gauge. - Uses these readings to diagnose the cause of poor gas mileage despite smooth running. This problem involves understanding measurement scales and interpreting gauge readings rather than algebraic computation.