A tell-tale or telltale is an indicator, signal, or sign that conveys the status of a situation, mechanism, or system.
Contents |
In a vehicle, a tell-tale is an indicator on or near the dashboard to inform the driver that a system or device is operating, switched on, or that a problem has occurred with the vehicle.
In a nautical or sailing context a tell-tale, sometimes known as a tell-tail, is a piece of cloth or fabric that is tied or attached to a stay, any of several wires which hold a mast in place on a sailboat. Usually there will be one tell-tale on the port stay and one on a starboard stay.
Tell-tales can also be attached to a sail, used as a guide when trimming (adjusting) a sail. On the mainsail tell-tales are on the leech (aft edge) and when trimmed properly should be streaming backwards. On the jib 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. If one tell-tale begins to spiral, it is indicating the sail has incorrect air flow on that side. To correct this the sail needs to move towards that side.
A tell-tale compass is a special compass installed in the ceiling of a cabin and which can be read from below, for example when one is resting on a bed, or from the side in a mirror showing the card's underside. According to Herman Melville's Moby Dick, a tell-tale refers to the cabin-compass, "because without going to the compass at the helm, the captain, while below, can inform himself of the course of the ship." [1]
The Phoenix spacecraft contains a tell-tale, developed by the University of Aarhus in Denmark, as part of its Meteorological Station.[2][3] It is a small tube that is deflected by the martian wind. The science payload’s stereo camera recorded images of the tell-tale that are used to determine wind direction and speed.[4]
In a steam locomotive the tell-tales are longitudinal holes drilled in the stays of the firebox to provide early warning of corrosion.
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 Railway 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[5].
In linguistics 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 language class is a finite subset 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 intelligence and machine language learning as well as linguistics.