Mouse dots-per-inch... how to tell?
Try the word MICKEY 
http://www.webopedia.com/TERM/M/mickey.html

Note, some OS (I believe Windows and Mac does this too) automatically change different "dot-per-inch" depending on the speed of human-user movement. if user move mouse fast, it increase "dot-per-inch". When user move mouse slowly, like doing fine painting on photoshop, it decrease so that user can control/move one or a few pixels.