" Absolute, true, and mathematical time, for itself, and from its own nature flows equably without regard to anything external, and by another name is called duration: relative, apparent, and common time, is some sensible and external (whether accurate or unequable) measure for duration by means of motion, which is commonly used instead of true time; such as an hour, a day, a month, a year. "

― John Gribbin , The Time Illusion (Kindle Single)