Immanuel Kant (1724-1804), the diminutive philosopher of Konigsberg, was so regular in his daily habits that people set their clocks by him when he passed. But one morning he woke up and saw that his own clock had stopped. He rewound it easily enough, but how could he find out the right time?  As he did every morning, the little professor walked across town to the house of his friend, taking exactly the same time as always, and when he arrived he noted the time on the parlor clock. He stayed for his usual visit, noted the time again and walked home where he was able to set his own clock correctly. How did he do that?

Hint: He decided that his own walking speed was so accurate that clocks should be set to him, not the other way around.