Quarter (qtr or Q) [7] : An informal unit of time equal to 1/4 hour or 15 minutes. This unit occurs in informal expressions of time, such as "quarter after 10" for 10:15
Russ Rowlett (Director), How Many? A Dictionary of Units of Measurement, Center for Mathematics and Science Education University of North Carolina, USA 2005. http://www.unc.edu/~rowlett/units/dictA.html, (Unit of Meas and Covr Factors - Amer) {608}