In honor of the Chicago marathon this weekend (and due in large part to Katie recovering from running in it...) we have a re-release of an episode about Kalman filters, which is part algorithm part elaborate metaphor for figuring out, if you're running a race but don't have a watch, how fast you're going. Katie's Chicago race report: miles 1-13: light ankle pain, lovely cool weather, the most fun EVAR miles 13-17: no more ankle pain but quads start getting tight, it's a little more effort miles 17-20: oof, really tight legs but still plenty of gas in then tank. miles 20-23: it's warmer out now, legs hurt a lot but running through Pilsen and Chinatown is too fun to notice mile 24: ugh cramp everything hurts miles 25-26.2: awesome crowd support, really tired and loving every second Final time: 3:54:35