Sighting Mark

Sighting Mark

 

a mark (or an object in a locality) used as a check when measuring the azimuth of astronomical or geodetic instruments. The Pulkovo type of sighting mark is extensively used. Such marks are long-focus collimating lenses with a focal distance of 100–200 m, mounted near the instrument being checked (to the north and south of it). Small circular apertures illuminated from the rear are located in special boxes at the focal points of the lenses. The directions to the apertures are ascertained using a micrometer eyepiece in the instrument. With this type of sighting mark a variation in the azimuth can be checked to an accuracy of 0.05”. [16-917^]

References in periodicals archive ?
Clark and Anderson's (http://www.dailymail.co.uk/femail/article-6096573/Look-away-Princess-Beatrice-Old-flame-Dave-Clark-shows-glamorous-new-wife.html) recent sighting marked the first time that the couple was spotted out in public since their nuptials.
And just a few miles down the road in Wales' smallest city, St David's more than 130 sightings have been logged at Oriel y Parc Gallery and Visitor Centre in St Davids, with each sighting marked with a pin on a map, showing how they are distributed along the Pembrokeshire Coast.
As shown in Figure 1, sightings within the observation period are arranged from the first to the last, and the time of the last sighting marked with the [t.sub.n].
Although there had been other documented wanderers as far back as the 1930s, her sighting marked the permanent return of the species to New York State.