Sine quadrant

[citation needed] It is impractical to sight a star through the front aperture unless it is on a fixed, stabilized mount relative to the half degree width of a very intense Sun.

At the apex—where the two graduated straight sides of the grid pattern meet in a right angle—is a thin cord strung through a pin hole and weighted with a small bead.

On one of the straight edges of the non-maritime quadrant (solid sheet form) are two alignment plates called hadafatani, each with a small central aperture (pinhole).

The maritime (navigation) version of these devices is skeletal in design rather than a solid sheet form, so as to limit buffeting or movement of the instrument from wind while in the operator's hand.

During the day, the Sun's altitude can be determined by aligning the apertures such that sunlight passes through both and projects a bright illuminated dot onto a surface (such as the user's finger or the screen plate of a mariner's backstaff).

When the apertures are optically aligned with the Sun, the user reads the angular measurement of the point where the graduated arc is bisected by the hanging plumb line.