Any discussion of Hartley Units makes me think of smoots - as in Olivor Smoots, a member of a MIT fraternity many years ago. After an evening of much liquid refreshment his brothers laid him end to end across the Harvard Bridge. Smoot was 5' 7", so that length is the official smoot. The fraternity brothers submitted a report to the Boston Police saying that the bridge is 364.4 smoots long. To this day the bridge is marked off in smoots, and if you get in an accident on the bridge the accident report states the location in smoots. Refer to the Wikipedia article for details and photos.