Vowel whose quality does not change over the duration of the vowel is called a monophthong. Monophthongs are sometimes called "pure" or "stable" vowels. A vowel sound that glides from one quality to another is called a diphthong, and a vowel sound that glides successively through three qualities is a triphthong. All languages have monophthongs and many languages have diphthongs, but triphthongs or vowel sounds with even more target qualities are relatively rare cross-linguistically. English has all three types: the vowel sound in "hit" is a monophthong , the vowel sound in "boy" is in most dialects a diphthong , and
Types of beacons Types of beacons Beacons are small devices that enable relatively accurate location within a narrow range. Beacons periodically transmit small amounts of data within a range of approximately 70 meters, and are often used for indoor location technology. Compared to devices based on Global Positioning System (GPS), beacons provide more accurate location information and can be used for indoor location. Various types of beacons exist, which can be classified based on their type of Beacon protocol, power solution and location technology. In December 2013, Apple announced iBeacon: the first beacon protocol in the market. iBeacon works with Apple's iOS and