Horizontal distances obtained by thermometric observations A. require slope correction B. require tension correction C. require slope and tension corrections D. do not require slope and tension corrections

The correct answer is: Horizontal distances obtained by thermometric observations do not require slope and tension corrections.

Thermometric leveling is a method of determining the horizontal distance between two points by measuring the difference in temperature between the two points. The temperature difference is used to calculate the height difference between the two points, and the height difference is then used to calculate the horizontal distance between the two points.

Slope and tension corrections are not required for thermometric leveling because the temperature difference is measured between two points that are at the same elevation. The temperature difference is not affected by the slope of the ground between the two points, and the temperature difference is not affected by the tension in the leveling rod.

Here is a brief explanation of each option:

• Option A: Slope correction is required for horizontal distances obtained by leveling when the ground is not level. The slope correction is used to account for the fact that the distance between two points on a slope is greater than the horizontal distance between the two points.
• Option B: Tension correction is required for horizontal distances obtained by leveling when the leveling rod is not vertical. The tension correction is used to account for the fact that the distance between the two ends of the leveling rod is greater than the horizontal distance between the two points when the leveling rod is not vertical.
• Option C: Slope and tension corrections are required for horizontal distances obtained by leveling when the ground is not level and the leveling rod is not vertical.
• Option D: Horizontal distances obtained by thermometric observations do not require slope and tension corrections because the temperature difference is measured between two points that are at the same elevation. The temperature difference is not affected by the slope of the ground between the two points, and the temperature difference is not affected by the tension in the leveling rod.