Correct option is D
In tachometric surveying, errors due to natural causes typically include:
Bad visibility: This can affect the accuracy of readings due to obstructions or poor weather conditions.
Unequal refraction: Variations in atmospheric refraction can cause errors in distance measurements.
Unequal expansion: Temperature changes can affect the expansion of materials and affect measurements.
Inaccurate levelling of instruments, however, is an error related to the handling and setup of the equipment, rather than a natural cause. It falls under operational errors or instrument errors, not natural causes.
Therefore, the correct answer is (d) Inaccurate levelling of instruments.
