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In a vigesimal place system, twenty individual numerals (or digit symbols) are used, ten more than in the decimal system. One modern method of finding the extra needed symbols is to write ten as the letter A, or A 20, where the 20 means base 20, to write nineteen as J 20, and the numbers between with the corresponding letters of the alphabet.
The apparent magnitudes of stars in the system are often used to determine the color indices B−V and U−B, the difference between the B and V magnitudes and the U and B magnitudes respectively. [1] The system is defined using a set of color optical filters in combination with an RMA 1P21 photomultiplier tube. [2]
Unertl Optical Company, Inc. was a manufacturer of telescopic sights in the United States from 1928 until 2008. They are known for their 10× fixed-power scopes that were used on the Marine Corps' M40 rifle and made famous by Marine Corps Scout Sniper Carlos Hathcock during the Vietnam War.
The sensitivity usually depends on the optical system, detectors and filters used. For each photometric system a set of primary standard stars is provided. A commonly adopted standardized photometric system is the Johnson-Morgan or UBV photometric system (1953). At present, there are more than 200 photometric systems. [citation needed]
A night vision device usually consists of an image intensifier tube, a protective housing, and an optional mounting system. Many NVDs also include a protective sacrificial lens, mounted over the front/ objective lens to prevent damage by environmental hazards, [ 1 ] while some incorporate telescopic lenses .
This is the model used in the Norwegian NALLADS air defense system. It combines the radar and RBS-70 missiles with 20 mm anti-aircraft guns to provide low-level air defense for the combat brigades of the Norwegian army. Mounted on a BV-206 all-terrain tracked vehicle, this version has an instrumented range of 50 km (31 mi).
A pair of marines scan with M16A4 rifles in Fallujah, Iraq (December 2004); the one in the foreground has an ITL MARS attached via a MIL-STD-1913 "Picatinny rail".. The ITL MARS (multi-purpose aiming reflex sight) is a gun sight that combines two sighting devices, a reflex sight and a laser sight, as well as a backup iron sight.
The intermediate survey (ITSS) is done between the second and the third year, and the scope of this survey depends on the age the vessel. Generally, it is an inspection of ballast more or less detailed. [clarification needed] For the chemical or oil carrier surveys are more intensive with the age.