A compass is an instrument used for navigation and orientation that shows direction relative to the geographic cardinal directions. A diagram called a compass rose shows the directions north, south and west on the compass face as abbreviated initials; when the compass is used, the rose. Compasses display markings for angles in degrees in addition to the rose. North corresponds to 0°, the angles increase clockwise, so east is 90° degrees, south is 180°, west is 270°; these numbers allow the compass to show magnetic North azimuths or true North azimuths or bearings, which are stated in this notation. If magnetic declination between the magnetic North and true North at latitude angle and longitude angle is known direction of magnetic North gives direction of true North. Among the Four Great Inventions, the magnetic compass was first invented as a device for divination as early as the Chinese Han Dynasty, adopted for navigation by the Song Dynasty Chinese during the 11th century; the first usage of a compass recorded in Western Europe and the Islamic world occurred around 1190.

The magnetic compass is the most familiar compass type. It functions as a pointer to "magnetic north", the local magnetic meridian, because the magnetized needle at its heart aligns itself with the horizontal component of the Earth's magnetic field; the magnetic field exerts a torque on the needle, pulling the North end or pole of the needle toward the Earth's North magnetic pole, pulling the other toward the Earth's South magnetic pole. The needle is mounted on a low-friction pivot point, in better compasses a jewel bearing, so it can turn easily; when the compass is held level, the needle turns until, after a few seconds to allow oscillations to die out, it settles into its equilibrium orientation. In navigation, directions on maps are expressed with reference to geographical or true north, the direction toward the Geographical North Pole, the rotation axis of the Earth. Depending on where the compass is located on the surface of the Earth the angle between true north and magnetic north, called magnetic declination can vary with geographic location.

The local magnetic declination is given on most maps, to allow the map to be oriented with a compass parallel to true north. The locations of the Earth's magnetic poles change with time, referred to as geomagnetic secular variation; the effect of this means. Some magnetic compasses include means to manually compensate for the magnetic declination, so that the compass shows true directions. There are other ways to find north than the use of magnetism, from a navigational point of view a total of seven possible ways exist. Two sensors that utilize two of the remaining six principles are also called compasses, i.e. the gyrocompass and GPS-compass. A gyrocompass is similar to a gyroscope, it is a non-magnetic compass that finds true north by using an fast-spinning wheel and friction forces in order to exploit the rotation of the Earth. Gyrocompasses are used on ships, they have two main advantages over magnetic compasses: they find true north, i.e. the direction of Earth's rotational axis, as opposed to magnetic north, they are not affected by ferromagnetic metal in a ship's hull.

Large ships rely on a gyrocompass, using the magnetic compass only as a backup. Electronic fluxgate compasses are used on smaller vessels. However, magnetic compasses are still in use as they can be small, use simple reliable technology, are comparatively cheap, are easier to use than GPS, require no energy supply, unlike GPS, are not affected by objects, e.g. trees, that can block the reception of electronic signals. GPS receivers using two or more antennae mounted separately and blending the data with an inertial motion unit can now achieve 0.02° in heading accuracy and have startup times in seconds rather than hours for gyrocompass systems. The devices determine the positions of the antennae on the Earth, from which the cardinal directions can be calculated. Manufactured for maritime and aviation applications, they can detect pitch and roll of ships. Small, portable GPS receivers with only a single antenna can determine directions if they are being moved if only at walking pace. By determining its position on the Earth at times a few seconds apart, the device can calculate its speed and the true bearing of its direction of motion.

It is preferable to measure the direction in which a vehicle is moving, rather than its heading, i.e. the direction in which its nose is pointing. These directions may be different if there is tidal current. GPS compasses share the main advantages of gyrocompasses, they determine true North, as opposed to magnetic North, they are unaffected by perturbations of the Earth's magnetic field. Additionally, compared with gyrocompasses, they are much cheaper, they work better in polar regions, they are less prone to be affected by mechanical vibration, they can be initialized far more quickly. However, they depend on the functioning of, communication with, the GPS satellites, which might be disrupted by an electronic attack or by the effect

One Man Army (TV series)

One Man Army is a reality television game show produced by Renegade 83 for the Discovery Channel. The show pits four men against various challenges to test intelligence, decision-making and physical strength; the host, Mykel Hawke, is a former Green Beret. The show begins with four contestants, the challenges test, in the following order, each of their Speed and Intelligence. In the first contest, the two best contestants with the fastest time go on to the next contest; the two weakest contestants go against each other in another elimination contest, the one who wins goes on with the first two. In the second contest, the three contestants' strength is tested, the weakest contestant is eliminated. In the third contest, the two contestants have a test of their ability to solve a puzzle or other intellectual challenge; the winner is given the title of "One Man Army" and $10,000. A contestant can "tap out" of a contest if they are unable to finish it. If a contestant taps out in the first contest, the third-best contestant automatically advances without having to complete an elimination contest.

Maze - the four contestants are given 15 seconds to view a maze having one entrance and one exit. They must crawl through the maze on their back as various distractions occur around them, including explosions, water, smoke and thorns. Urban Combat - standing in the back of a moving pick up truck, the contestants must shoot 10'people' targets using a automatic machine gun once they have hit every target, run to a wall where they have six shots with a grenade launcher to try and shoot into a building. "Dead Heat" - crawl hand-over-hand along a rope overhead of them to infiltrate the target area, traverse a debris-laden obstacle course, arrive at a firing range, hit a square target with a semi-auto handgun. Extended in the first season to include 3 targets per contestant. Water Coffin - Escape from a water-filled box by sawing through the 4 bars of the grate. Lasers - Negotiate a laser field to obtain a briefcase, handcuffed to the contestants wrist and must be brought back through the laser field to the start point.

Ice Breaker - Extract 5 keys frozen into blocks of ice to unlock the door to the ice truck. Two ice blocks contain a screwdriver, respectively; the contestants can choose whether or not to attempt to free tools to assist in the extraction of the keys. Tug of War; the three contestants are chained to each other and one of them must be able to reach a bell switch 3 times. The remaining two have to try to reach one of the bells, the one that fails is eliminated. Breach. Get through two doors, a concrete-and-rebar reinforced brick wall, a drywall board wall, two more doors, sometimes using brute force, in some cases with tools. One of the doors is a "trick" door, it is an ordinary door, unlocked, if they check it they can turn the knob and walk through as opposed to using a sledge hammer to break the door down. Walls. Contestants must carry heavy packs over and under a series of 5 walls. Ice Breaker. See Speed challenge. Used for speed challenges, featured in S1E7 as strength challenge. Cell - Two contestants are locked in cells with various items such as clothing, hangars, a bed, a chair, etc.

The objective is to build an item which will allow them to reach nine feet out of their cell and snag the key to their cell. First one to unlock their cell and strike the bell wins the game. Waterboarding - The contestants are chained to a board that slides into a cold pool, they are shown a series of lights. They can ask to be pulled back up for air at any time. Once they set the series they push a button on the board. After 6 selections, the seventh is the combination to unlock their chain. Bomb Squad - This challenge tests the contestants ability to remember the steps required to defuse 4 different bombs, they are each given 90 seconds to study the steps fitted with protective gear and must defuse a pressure plate trigger on a bridge bomb, cut the wires in the correct sequence on an area IED, open and locate the right wire on a time bomb, access and disable a booby-trapped car bomb. Observe and Report - The contestants are delivered to a staged area where they are given 3 minutes to observe the people and circumstances around them.

When the timer runs out, the contestants deliver their'package' return. They are presented with up to ten questions regarding what they have observed; the contestant with the most correct responses wins the challenge. In the event that a contestant has a sufficiently higher number of correct answers than the other such that the other contestant cannot win the challenge ends. Safe Cracking - The contestants are suspended upside down by their ankles and must open 4 safes containing parts of a handgun that they must assemble and fire at a target to free themselves; the safes each have clues that will reveal the nature of the task necessary to open the lock


Battleby is a country house in Perth and Kinross, Scotland. It is located in the parish of Redgorton, 1 kilometre west of Luncarty and 6 kilometres north of Perth; the 19th-century house is occupied by Scottish Natural Heritage, is protected as a category B listed building. The grounds are listed on the Inventory of Gardens and Designed Landscapes in Scotland, the national listing of significant gardens, for their important plant collection; the estate is named after the Battle of Luncarty, recorded by Hector Boece as a battle between Scots and Danes in 990, although a historian has doubted whether such a battle occurred. The Battleby estate was acquired in the 19th century by the Maxtone-Graham family; the house was built to designs by the Perth-based architect David Smart. The design of the house shows the influence of Alexander Thomson; the Grahams laid out the grounds of the house, planted many of the trees which still remain. In the 19th century the house was leased, served as a hospital during the First World War.

Battleby was bought in 1947 by Sir Alexander Cross, who built up an important plant collection in the grounds. In 1970 the house was purchased by the Countryside Commission for Scotland, a public body with responsibility for natural heritage, was converted for use as their national headquarters, with a visitor centre designed by Morris and Steedman. In 1992, the Countryside Commission for Scotland was replaced with a new body, Scottish Natural Heritage. SNH moved their main headquarters to Inverness, Battleby now serves as a local office within the Tayside and Grampian Area Management Unit