A
tell-tale is a reference indicator or a sign that clearly signals that something else is true or is about to happen.
In a nautical or
sailingSailing is the art of controlling a boat with large foils called sails. By changing the rigging, rudder, and sometimes the keel or centre board, a sailor manages the force of the wind on the sails in order to change the direction and speed of a boat...
context a tell-tale, sometimes known as a tell-tail, is a piece of cloth or fabric that is tied or attached to a
stayStays are the heavy ropes, wires, or rods on sailing vessels that run from the masts to the hull, usually fore-and-aft along the centerline of the vessel...
, any of several wires which hold a
mastThe mast of a sailing ship is a tall, vertical, or near vertical, spar, or arrangement of spars, which supports the sails. Large ships have several masts, with the size and configuration depending on the style of ship....
in place on a
sailboatA sailboat or sailing boat is a boat propelled partly or entirely by sails. The term covers a variety of boats, larger than small vessels such as sailboards and smaller than sailing ships, but distinctions in size are not strictly defined and what constitutes a sailing ship, sailboat, or a smaller...
. Usually there will be one tell-tale on the
portPort is the nautical term that refers to the left side of a ship, as perceived by a person on board the ship and facing towards the bow . The port side of a vessel is indicated with a red navigation light at night.The term is also used on aircraft, spacecraft, and analogous...
stay and one on a
starboardStarboard is the nautical term that refers to the right side of a vessel as perceived by a person on board a vessel and facing the bow . The equivalent for the left-hand side is port. The starboard side of a vessel is indicated with a
green navigation light at...
stay.
Tell-tales can also be attached to a
sailA sail is any type of surface intended to generate thrust by being placed in a wind—in essence a vertically-oriented wing. Sails are used in sailing.-History of sails:...
, used as a guide when trimming (adjusting) a sail.
A
tell-tale is a reference indicator or a sign that clearly signals that something else is true or is about to happen.
Sailing
In a nautical or
sailingSailing is the art of controlling a boat with large foils called sails. By changing the rigging, rudder, and sometimes the keel or centre board, a sailor manages the force of the wind on the sails in order to change the direction and speed of a boat...
context a tell-tale, sometimes known as a tell-tail, is a piece of cloth or fabric that is tied or attached to a
stayStays are the heavy ropes, wires, or rods on sailing vessels that run from the masts to the hull, usually fore-and-aft along the centerline of the vessel...
, any of several wires which hold a
mastThe mast of a sailing ship is a tall, vertical, or near vertical, spar, or arrangement of spars, which supports the sails. Large ships have several masts, with the size and configuration depending on the style of ship....
in place on a
sailboatA sailboat or sailing boat is a boat propelled partly or entirely by sails. The term covers a variety of boats, larger than small vessels such as sailboards and smaller than sailing ships, but distinctions in size are not strictly defined and what constitutes a sailing ship, sailboat, or a smaller...
. Usually there will be one tell-tale on the
portPort is the nautical term that refers to the left side of a ship, as perceived by a person on board the ship and facing towards the bow . The port side of a vessel is indicated with a red navigation light at night.The term is also used on aircraft, spacecraft, and analogous...
stay and one on a
starboardStarboard is the nautical term that refers to the right side of a vessel as perceived by a person on board a vessel and facing the bow . The equivalent for the left-hand side is port. The starboard side of a vessel is indicated with a
green navigation light at...
stay.
Tell-tales can also be attached to a
sailA sail is any type of surface intended to generate thrust by being placed in a wind—in essence a vertically-oriented wing. Sails are used in sailing.-History of sails:...
, used as a guide when trimming (adjusting) a sail. On the
mainsailA mainsail is the most important sail raised from the main mast of a sailing vessel.On a square rigged vessel, it is the lowest and largest sail on the main mast....
tell-tales are on the leech (aft edge) and when trimmed properly should be streaming backwards. On the
jibA jib is a triangular staysail set ahead of the foremast of a sailing boat. Its tack is fixed to the bowsprit, to the bow, or to the deck between the bowsprit and the foremost mast...
there are tell-tales on both sides of the luff of the sail. As a general guide, the windward tell-tale should stream aft (backwards) with an occasional lift, the leeward front tell-tale should stream aft.
Space
The
PhoenixPhoenix was a robotic spacecraft on a space exploration mission on Mars under the Mars Scout Program. The Phoenix lander descended on Mars on May 25, 2008...
spacecraft contains a tell-tale, developed by the
University of AarhusAarhus University , located in the city of Århus, Denmark, is Denmark's second oldest and second largest university ....
in
DenmarkDenmark is a Scandinavian country in Northern Europe and the senior member of the Kingdom of Denmark. It is the southernmost of the Nordic countries; southwest of Sweden and south of Norway, and it is bordered to the south by Germany. Denmark borders both the Baltic and the North Sea...
, as part of its
Meteorological Station. It is a small tube that is deflected by the
martianMars is the fourth planet from the Sun in the Solar System. The planet is named after Mars, the Roman god of war. It is also referred to as the "Red Planet" because of its reddish appearance, due to iron oxide prevalent on its surface....
wind. The science payload’s
stereo cameraA stereo camera is a type of camera with two or more lenses. This allows the camera to simulate human binocular vision, and therefore gives it the ability to capture three-dimensional images, a process known as stereo photography. Stereo cameras may be used for making stereoviews and 3D pictures...
recorded images of the tell-tale that are used to determine wind direction and speed.
Railroad
In a
steam locomotiveA steam locomotive is a locomotive powered by steam. The term usually refers to its use on railways, but can also refer to a "road locomotive" such as a traction engine or steamroller....
the tell-tales are
longitudinalLongitudinal may refer to:* Longitudinal engine, an internal combustion engine in which the crankshaft is oriented along the long axis of the vehicle, front to back...
holes drilled in the stays of the firebox to provide early warning of
corrosionCorrosion is the disintegration of a material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means a loss of electrons of metals reacting with water and oxygen. Weakening of iron due to oxidation of the iron atoms is a...
.
A tell-tale is also a series of ropes suspended over the tracks above the height of a boxcar. These ropes are intended to give warning to a brakeman on the roof of the train that the train is approaching a low-clearance obstacle, such as a tunnel or a bridge. A
Chesapeake and Ohio RailwayThe Chesapeake and Ohio Railway was a Class I railroad formed in 1869 in Virginia from several smaller Virginia railroads begun in the 19th century. Led by industrialist Collis P...
tell-tale had 17 of these ropes hanging from a tube suspended across the track, the bottom of the ropes 12" lower than the height of the obstruction, and placed 100 to 300 feet before the obstruction. On British Mark 1 carriages, a Tell Tale connects the emergency (communication) cord or chain to the train line to facilitate an emergency stop.
Linguistics
In
linguisticsLinguistics is the scientific study of natural language. Linguistics encompasses a number of sub-fields. An important topical division is between the study of language structure and the study of meaning...
a tell-tale is a string of characters that occurs only within one language within a group of languages. A reader can be completely certain which language they are reading if he or she comes across a tell-tale. In this sense, a tell tale is a dead give away of what the language is.
More formally, a tell-tale of a member L of some
languageA formal language is a set of words, i.e. finite strings of letters, symbols, or tokens. The set from which these letters are taken is called the alphabet over which the language is defined...
class is a
finiteIn mathematics, finite set is a set that has a finite number of elements. For example,is a finite set with five elements. The number of elements of a finite set is a natural number , and is called the cardinality of the set. A set that is not finite is called infinite...
subsetIn mathematics, especially in set theory, a set A is a subset of a set B if A is "contained" inside B. Notice that A and B may coincide...
of
L such that no other language containing the subset in the class is a proper subset of
L. In other words, a tell-tale is a finite subset that makes a language being a minimal consistent one in the class. The term is used in the field of
artificial intelligenceArtificial intelligence is the intelligence of machines and the branch of computer science which aims to create it. Textbooks define the field as "the study and design of intelligent agents,"...
and
machine language learningMachine learning is a scientific discipline that is concerned with the design and development of algorithms that allow computers to learn based on data, such as from sensor data or databases. A major focus of machine learning research is to automatically learn to recognize complex patterns and...
as well as linguistics.