line passing through the objective lens and the eye-piece of a dumpy or tilting level
line parallel to the mean spheroidal surface of earth
line passing through the center of cross hairs and the center of eye piece
Discuss in Comment
"Scientists dream about doing great things. Engineers do them."
PSC Advertisement ⏩ | Federal PSC | Bagmati PSC | PSC Karnali | PSC Lumbini | PSC Sudurpaschim | PSC Gandaki | PSC State 1.