Niigata seiki LEVELNIC DL-S3 DL-BW, Руководство по эксплуатации

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<Functions of 0-Call and 1/2-Call>
Since the level works acutely on the gravity of the earth, the zero point of level can be known by
the following way of thinking.
Suppose there is a slope of angle
θ
with respect to the horizontal plane.
Place on that slope a board with a weight suspended on thread.
Then, the weight inclines toward side A of the board by angle
θ
from the line extended
orthogonally from the slope.
When the board is turned over 180º, the weight now inclines toward side B of the board by angle
θ
from the line extended orthogonally from the slope.
Consequently, it results that the board can detect an angle of 2 x
θ
when it is turned over 180º,
even if there is no absolute reference (line extended orthogonally from the slope) available. Since
θ
can be known when 2 x
θ
is halved, the horizontal plane is also found. It is for this reason that,
when the board is turned over 180º, the actual inclination is indicated twice as large, assuming
that one inclined side is at zero in the leveling. When this double indication is halved, the product
will represent the inclination of that location, and if we adjust the inclination of the slope (object
under measurement) in such a manner that the halved indication will become zero, that plane will
become level.
Conversely, if a device that possesses an absolute reference gets to have that reference deviated
for any reason, it is likely that we may be using the device without knowing the presence of that
deviation.
Weight
Weight
Gravity
Gravity