The quadrant curve or ‘qaus’, is a bow-shaped curve formed from the central quadrant. Grids which come down
from the vertical axis to the curve become the adjacent side of a right triangle which form Pythagoras’ theorem. [See
Figure 1, this side is marked Y]. In the use of the sine quadrant, a grid reading on this scale from the angle of the
curve to the vertical axis represents the value of the ratio of the sine functions. While the grids that are projected
from the horizontal axis to the curve become the opposite side, marked by X in Fig. 1. Grid reading on this scale
from the angle of curve of the horizontal axis represents the value of the cosine ratio functions. Each grid represents
the ratio of horizontal and vertical angles which are read on the curve (0° to 90 °) and centered on the origin of the
quadrant. In Figure 1, the angle θ of the triangle POQ is the angle formed by the ratio of the side adjacent to the
opposite side, while the hypotenuse measures R = 60 units. Hence, the triangle POQ gives the value;
sin θ = 6 0
X (1)
cos θ = 6 0
Y (2)
In the use of the sine quadrant, the function of the cosine angle is shown as a function of the complementary angle
of sine functions. If the angle is measured on the curve as θ, then the complementary angle is (90°- θ). Sine angle
is read from the initial curve, starting at 0° and the ratio following the horizontal grid to the vertical axis. Whereas
the cosine angle starting at the end of the curve at a value of 90° (read as 0° for cosine functions). However, if the
cosine angle needs to be determined at the initial point of curve (starting at 0°), the ratio should be read from the
horizontal axis using the vertical grid. This operations gives the correlations as follows;
cos θ = sin (90 - ° θ) (3)
The intersection of the vertical and horizontal grid will give the angle of tangent functions.
Angle measurement scale on the curve of the quadrant is marked starting from 0° to 90°, can also be used to
measure the scale of unit hours from 0 hour to 12 hours and the commencement date of the constellation starting
from 01 degrees to 30 degrees for every month. All units of measurement scales can be read up to the estimation of
the minimum value depending on the scale of the curve. For example, degree units with a small interval of 1°, can
be estimated up to a value of 1
8
(equivalent to 7.5 arc minutes). As for unit hours with a small interval equivalent
to 4 minutes, the reading can be estimated up to 30 seconds.