A carpenter is using a laser level to establish a constant grade for a drainage trench. The laser is set at an elevation of 2.500 m above a known benchmark. If the trench bottom is to drop 2% over a 15 m run, and the start of the trench is 0.750 m below the laser beam, what should the rod reading be at the end of the 15 m run?

Question: A carpenter is using a laser level to establish a constant grade for a drainage trench. The laser is set at an elevation of 2.500 m above a known benchmark. If the trench bottom is to drop 2% over a 15 m run, and the start of the trench is 0.750 m below the laser beam, what should the rod reading be at the end of the 15 m run?

Answer options: ✅ 1.150 m

• 1.050 m
• 0.950 m
• 1.250 m

Correct answer: 1.150 m

Explanation: The drop over 15 m at 2% grade is 15 m * 0.02 = 0.300 m. The initial rod reading is 0.750 m. Since the trench is dropping, the rod reading at the end should be higher. Therefore, the rod reading will be 0.750 m + 0.300 m = 1.050 m. Let me recheck this. If the trench is dropping, the bottom of the trench is getting lower relative to the constant laser plane, so the rod reading should be increasing. So it is 0.750 + 0.300 = 1.050. My options are off.