Paadham = 4 Quarters of each nakshatra / Link / Name / Calculator

 The space occupied by each naksatra (in the great circle) is divided into four equal quarters.

 Since there are 27 nakshatras, there are 108 nakshatra quarters (27 x 4 = 108) in total with

 each quarter spanning 3 degrees and 20 minutes of the great circle.

 Each quarter of each nakshatra will never span two rasis; each quarter will be part of one and only one rasi.

 Each such nakshatra quarter is referred to as a Nakshatra Paadham or Nakshatra Pada.

http://www.bhaktivedantacollege.org/bvc_site/resources_services/articles/pdfs/jyotish/formal/english/27_nakshatra_padas.pdf

http://kuberastrology.blogspot.in/2010/05/nakshatra-finder-nakshatra-and-rashi.html
http://www.downloadplex.com/tags/nakshatra+pada+calculator/Page-1-0-0-0-0.html