ANS:A -

For example, You are on the sloped surface and you are measuring horizontal distances, so here one end is fixed and when you move to the other end on a sloped surface, there will be the difference in elevations from two ends of the chain,

NOW, HERE WILL COME ERROR BECAUSE OF THE EARTHS CURVATURE, and that error is cumulative (an error will add with slope length). so the formula is h2/2l = d2/2*30 = d2/60 , (d= verticle distance) Formula Of Alignment correction = h Square /2L,
Length of Chain (L)= 30 m.
= h Square / 2*30 m = h Square / 60 m.

(Right Answer = d square / 60 m). Slope correction= h^2/2D = d^2/2*30 = d^2/60.