Basic principle of the direct determination of the plumb line's

Does a plumb line always point toward the center of the earth or

Aberration (astronomy) - Wikipedia

Plumb Line - an overview

4. Measuring Vertical Angles And Slopes

Explain why a plumb bob will not hang exactly in the direction of

Plumb Line - an overview

principle of survey

Does a plumb line always point toward the center of the earth or

Linear measurement

Open Access Surveying Library - Chapter G. Theodolite and Total