Zhou Chaochen, C. A. R. Hoare and Anders P. Ravn, A Calculus of Durations, Information Processing Letters, 40(5):269–276, December 1991. /wiki/Zhou_Chaochen
Zhou Chaochen and Michael R. Hansen, Duration Calculus: A Formal Approach to Real-Time Systems. Springer-Verlag, Monographs in Theoretical Computer Science, An EATCS Series, 2003. ISBN 3-540-40823-1. /wiki/Zhou_Chaochen
DCVALID: A tool for model-checking Duration Calculus formulae, TIFR, India. http://www.tcs.tifr.res.in/~pandya/dcvalid.html
IDLVALID: Model checking dense time Duration Calculus formulae, TIFR, India. http://www.tcs.tifr.res.in/~pandya/idlvalid.html