In Korea, it has been adopted the normal height as a height in vertical reference system which is based on normal gravity.
But, for the calculation of accurate result on benchmark, it has to be adopted the orthometric height considering with orthometric correction which is based on gravity observation.
For this study area was selected in Gangwon province and gravity surveys were carried out according to four routes which composed of south and north routes and Korean first benchmark line and second benchmark line respectively.
Four formulas, M. Nassar, C. Hwang1, C. Hwang2 and Strang Van Hees were used to calculate orthometric correction. And the calculation results show that Strang Van Hees' formula is best optimum in Korean mountainous area and the orthometric correction shows 53mm when the height difference is 870m.
So orthometric correction is confirmed necessary to calculate orthometric correction at Korean benchmarks.