| This alignment is performed with the aid of an alidade, or sight rule, a straightedge fitted with simple sights. |
|
| On the back of the astrolabe, we use the alidade and the two pinholes to point a star. |
|
| With the aid of a double alidade with sights, it was possible to measure angles whose accuracy, however, did not exceed? |
|
| A pointer, called an alidade, was pivoted at the centre of the disk. |
|
| A variation of the instrument, the marine astrolabe, was designed exclusively for measuring vertical angles to the stars and was limited to an alidade and a circle of degrees. |
|
| An alidade can be seen in the lower right illustration of the Persian astrolabe above. |
|
| At choice two different sighting telescopes with vertical circle are available: The autoreduction telescope of the MEDIA and the standard telescope of the MEJUN alidade. |
|
| A survey instrument consisting of an alidade, telescope, and vertically and horizontally mounted graduated circles, used to measure vertical and horizontal angles. |
|
| Planispheric astrolabe made of brass and comprising four main pieces: a box or 'mother' made up of five sheets that represent different latitudes, a network or 'spider' with indicators for 24 stars and an alidade. |
|
| An optical plummet, built into either the tribrach or alidade of total station instruments, permits accurate centering over a point. |
|
