  a tell-tale or telltale is an indicator, signal, or sign that conveys the status of a situation, mechanism, or system.  ==transportation== ===automobiles===  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. the name itself indicates that it tells you a small story related to the vehicle. so a tell tale is a small story for the driver. for example: when you see the right or the left indicator it tells the driver a small tale that the vehicle is about to turn followed by its turning and finally it has completed the turn when the light goes off. similarly, when there is an error, its tells you where the error is when possible. ===sailing=== thumb|a tell-tale in a nautical or sailing context a tell-tale, sometimes known as a tell-tail, is a piece of yarn or fabric attached to a stay, any of several wires which hold a mast in place on a sailboat. they are used in pairs, on each side of the jib; 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 the opposite side. "tiller to tatteling tail" is a good phrase to remember which direction to push the tiller when the tell tale is spiraling. a tell-tale compass is a special compass installed in the ceiling of a cabin and which can be read from below. according to 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."  ===space=== the phoenix spacecraft 
English_phrases Formal_languages Measuring_instruments