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putting the curvature of the  earth in to account  how  leveling is carried out?
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The formula for computing the combined effect of curvature and refraction is:

C + R = 0.021K2

Where C = correction for curvature

R = correction for refraction

K = sighting distance in thousands of feet

How to eliminate error due to Curvature and Refraction

  1. Proper field procedures (taking shorter shots and balancing shots) can practically reduce errors

  2. Wherever possible, staff readings should be kept at least 0.5 m above the ground,

  3. Using short observation distances (25 m) equalized for backsight and foresight

  4. Air below is denser than air above Air below is denser than air above, Line of sight is bent downward which Negates earth curvature error by 14%.

  5. Simultaneous Reciprocal Trigonometrical Heighting

  6. Observations made at each station at exactly the same time, cancels the effects of curvature and refraction

17yrs in the field of civil engineering as a land surveyor completing projects requiring dead nuts accuracy spanning tens of miles horizontally as well as hundreds of feet vertically using astonishingly precise instrumentation to calculate each known empirically definable variable including adjustments for thermal atmospheric refraction and optical refractory parallax , while maintaining tolerances as little as one one/hundredth of a foot.

Never have i visually observed, nor do my instruments indicate evidence of, and NEVER have i “adjusted” my collected observational field data or implemented any equation variable to account for a spherical geography.

The phenomenon asserting spherical global geography is not included as applied to engineering and construction in the physical world.

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It is called Geodetic Survey..
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