most advanced among heart rate monitors at the time of its release in 2004. It has, among other features, rate-to-rate recording of heart rate, an altimeter based on air pressure, calculation of EPOC and training effect and support for external POD devices measuring speed and distance. Suunto T3 (and its C and D versions) offered many advanced training properties with much lower price than T6. The T4 (with also C and D versions) was close the same as the T3, but it added an electronic coach function. There were also T1 and T1C, a very basic heart monitors in T-series. All T-series versions have gone out of production until 2012. The M-series are a successor of T-series (except for T6). The M-series is more of an entry-level fitness lineup, while T-series was more aimed at sports training. The M-series include the basic heart monitors M1 and M2 (same watch, different heart rate strap) and M4 and M5 with more advanced functions, most of which electronic coaching for specific goals, such as weight control or improving physical performance. M4 went out of production in 2013. Suunto Quest is a heart rate monitor aimed at sports training. Suunto Ambit series, with the first version released in 2012 and later having included Ambit2 and Ambit3 lineups. These include GPS, ABC-functions, rechargeable battery, advanced training functions (in training functions Ambit is a successor of T6) and updatable software. User can modify many of the functions of Ambit according to individual preferences. Different apps are also available, and users can also create their own apps. Limited in production amounts, Ambit2 S Black Limited Edition has been available from June 2015. Ambit3 adds smartphone connectivity as its main improvement. On September 29, 2015 Ambit3 Peak Nepal Edition was released. There is no other difference between this and the normal version besides "Nepal Edition" text on the screen and a bit different bezel, but of every watch sold are donated to Red Cross for humanitarian aid and rebuilding in Nepal. On January 7, 2016 Ambit3 Vertical was introduced. It adds more comprehensive tracking of vertical movement and introduces a redesigned body. Suunto Core is an ABC-watch (A=altitude, B=barometer, C=compass). Since its release in 2007 there has been more than 30 different versions of Core. All of them have the same functions, but their external appearance differ. Most versions have plastic frames, but some are made of aluminum