Tell-tale

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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 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.

Space

The Phoenix spacecraft contains a tell-tale, developed by the University of Aarhus in Denmark, as part of its Meteorological Station.^[1][2] 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.^[3]

Railroad

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^[4].

Linguistics

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.

See also

• Language identification in the limit

References

1. ^ Mars Simulation Laboratory, University of Aarhus, Denmark, The Telltale project, http://www.marslab.dk/TelltaleProject.html 
2. ^ Slashdot 27may2008, Mars Probe Brings the "Weather Rock" New Respect, http://science.slashdot.org/article.pl?sid=08/05/27/153240 
3. ^ Nasa Press Kit/May 2008, ed., Phoenix Landing Mission to the Martian Polar North, http://www.nasa.gov/pdf/226508main_phoenix-landing1.pdf 
4. ^ Parkin Keith, British Rail Mark 1 Coaches 1991