Tibet-Encyclopaedia (s.v. Kalenderrechnung); "Tibetische Kalenderrechnung (lnga bsdus)":http://www.tibet-encyclopaedia.de/kalenderrechnung.html by Dieter Schuh (b. 1942) (accessed: 2013-10-22)
introduction to the different Tibetan calendar systems and related software is provided by Edward Henning on "Kālacakra":http://www.kalacakra.org/ (accessed: 2013-10-22)