Derailleur gears by 13 drive-train. Most road bicycles have two chainrings, and touring bicycles commonly have three. The rear derailleur serves double duty: moving the chain between rear sprockets and taking up chain slack caused by moving to a smaller sprocket at the rear or a smaller chainring by the front derailleur. In order to accomplish this second task, it is positioned in the path of the bottom, slack portion of chain. Sometimes the rear-derailleurs are re-purposed as chain tensioners for single-speed bicycles that cannot adjust chain tension by a different method. Although variations exist, as noted below, most rear derailleurs have
Units of measurement in France before the French Revolution (league) had a number of variations, particularly the "aune" (which was used to measure cloth The "loi du 19 frimaire an VIII" (Law of 10 December 1799) states that one decimal metre is exactly 443.296 French lines, or "3 pieds 11.296 lignes de la "Toise du Pérou"". Thus the French royal foot is exactly 9000/27,706 metres (about 0.3248 m). In Quebec, the surveys in French units were converted using the relationship 1 "pied" (of the French variety, the same word being used for English feet as well) = 12.789 English inches. This makes the Quebec "pied" very slightly smaller (about