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The water level at each end of the tube will be at the same elevation, whether the two ends are adjacent or far apart, so a line between them will be horizontal at its midpoint and a shed base, building foundation or similar structure laid out using several such lines will be "horizontal" within building tolerances on any scale over which use ...
In 1914 and 1915, the Forestry Quarterly published a series of articles on the use of the Abney level. [6] [7] [8] These tutorial articles remain useful today, but the primary reference for usage is the 1927 Abney Level Handbook. [3] The Abney level is typically used at the eye height of the surveyor, either hand-held or mounted on a staff at ...
The surveyor does this with the use of a bull's eye level built into the instrument mount. The surveyor looks through the eyepiece of the telescope while an assistant holds a vertical level staff which is graduated in inches or centimeters. The level staff is placed with its foot on the point for which the level measurement is required.
[clarification needed] It must also be corrected for errors (i.e., bad soundings,) and for the effects of tides, heave, water level [34] [35] [36] salinity and thermoclines (water temperature differences) as the velocity of sound varies with temperature and salinity and affects accuracy. Usually the surveyor has additional data collection ...
U.S. Bureau of Land Management map showing the principal meridians of Ohio, Indiana, and Illinois. The fourth principal meridian, set in 1815, [1] is the principal meridian for land surveys in northwestern Illinois and west-central Illinois, [2] and its 1831 [3] extension is the principal meridian for land surveys in Wisconsin and northeastern Minnesota.
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