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  2. Luopan - Wikipedia

    en.wikipedia.org/wiki/Luopan

    A red wire or thread that crosses the earth plate and heaven dial at 90-degree angles is the Heaven Center Cross Line, or Red Cross Grid Line. [1] This line is used to find the direction and note position on the rings. Small feng shui compass, c. 1800–1894, from the Oxford College Archives of Emory University.

  3. Theodolite - Wikipedia

    en.wikipedia.org/wiki/Theodolite

    The pibal theodolite uses a prism to bend the optical path by 90 degrees so the operator's eye position does not change as the elevation is changed through a complete 180 degrees. The theodolite is typically mounted on a rugged steel stand, set up so it is level and pointed north, with the altitude and azimuth scales reading zero degrees.

  4. Combination square - Wikipedia

    en.wikipedia.org/wiki/Combination_square

    [1] [2] Other names for the tool include adjustable square, combo square, and sliding square. The most common head is the standard head, which is used as a square for marking and testing 90° and 45° angles. [3] The other common types of head are the protractor head, and the centre finder head. [4]

  5. Oblique projection - Wikipedia

    en.wikipedia.org/wiki/Oblique_projection

    The projectors in oblique projection intersect the projection plane at an oblique angle to produce the projected image, as opposed to the perpendicular angle used in orthographic projection. Mathematically, the parallel projection of the point ( x , y , z ) {\displaystyle (x,y,z)} on the x y {\displaystyle xy} -plane gives ( x + a z , y + b z ...

  6. Special right triangle - Wikipedia

    en.wikipedia.org/wiki/Special_right_triangle

    Set square shaped as 45° - 45° - 90° triangle The side lengths of a 45° - 45° - 90° triangle 45° - 45° - 90° right triangle of hypotenuse length 1.. In plane geometry, dividing a square along its diagonal results in two isosceles right triangles, each with one right angle (90°, ⁠ π / 2 ⁠ radians) and two other congruent angles each measuring half of a right angle (45°, or ...

  7. Goniometer - Wikipedia

    en.wikipedia.org/wiki/Goniometer

    To measure an angle between the beam and the blade of 90° or less, the reading may be obtained directly from the graduation number on the dial indicated by the mark on the swivel plate. To measure an angle of over 90°, subtract the number of degrees as indicated on the dial from 180°, as the dial is graduated from opposite zero marks to 90 ...

  8. Angle of incidence (optics) - Wikipedia

    en.wikipedia.org/wiki/Angle_of_incidence_(optics)

    The angle of incidence, in geometric optics, is the angle between a ray incident on a surface and the line perpendicular (at 90 degree angle) to the surface at the point of incidence, called the normal. The ray can be formed by any waves, such as optical, acoustic, microwave, and X-ray. In the figure below, the line representing a ray makes an ...

  9. Try square - Wikipedia

    en.wikipedia.org/wiki/Try_square

    A try square or try-square is a woodworking tool used for marking and checking 90° angles on pieces of wood. Though woodworkers use many different types of square, the try square is considered one of the essential tools for woodworking. [1] The square in the name refers to the 90° angle.