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Saddle up your imagination. This is a unit to measure distance traveled per unit of fuel. You might ask what the hell is relevance of rods and hogsheads with distance and units.

Well, a hogshead is designed to hold volumes equal to two barrel worth of wine or gasoline (petrol as we Indians call it). Two barrels is exactly equal to 63 US gallons (1 US gallon = 3.7854118 liters) or about 52.5 imperial gallons. So a hogshead is exactly equals to 63 US gallons.

Rods: A rod is a traditional unit of distance which equals to 5.5 yards (16 feet 6 inches or exactly 5.0292 meters). This has nothing to do with ‘khamba’ as we call it in slang Hindi ;-).

The Parliamentary Statute of 1592 defined a mile to be 320 rods.

So to calculate rods to hogsheads from miles/gallon we use this..

Miles/Gallon * Gallons/Hogshead * Rods/Mile = Rods to the Hogshead

If your car runs 44 MPG then you would convert it like this..

44/1 * 63/1 * 320/1 = 887040 rods to the hogshead

Rod: Historic background

Before the Norman conquest of 1066 (http://en.wikipedia.org/wiki/Norman_Conquest) the rod and furlong were the basic distance units used by the Anglo-Saxon residents of England. The Anglo-Saxons called it the gyrd, the name which is derived from other unit, the yard. The word rod means pole or a perch in Saxon. The Norman preferred to call the gyrd a pole or a perch (a word of French origin, meaning a pole; see perche).The length of the rod was well established at about 5 meters at least as early as the eighth century. Scholars are not sure how it was related to shorter units. It may have been considered equal to 20 “natural” feet (actual foot lengths; see foot), or it may have been measured “by hand” as 30 shaftments. In any case, when the modern foot became established in the twelfth century, the royal government did not want to change the length of the rod, since that length was the basis of land measurement, land records, and taxes. Therefore, the rod was redefined to equal 16.5 of the new feet. This length was called the “king’s perch” at least as early as the time of King Richard the Lionheart (1198). Although rods and perches of other lengths were used locally in Britain, the king’s perch eventually prevailed. The relationship between the rod and the other English distance units was confirmed again by the Parliamentary statute of 1592, which defined the statute mile to be either 320 rods or 1760 yards, thus forcing the rod to equal exactly 5.5 yards or 16.5 feet.

furlong: A furlong equals 40 rods, which is exactly 10 chains, 220 yards, 660 feet, or 1/8 mile. One furlong is exactly 201.168 meters, so a 200-meter dash covers a distance very close to a furlong. The length of horse races is often stated in furlongs.

perche or perch: a traditional unit of distance in French North America. The perche equals 18 pieds or 3 toises. By legal definition in Canada this equals 19.1835 English feet or 5.847 13 meters.

shaftment: an old English unit of distance equal to 2 palms. A shaftment is the distance from the tip of the outstretched thumb to the opposite side of the palm of the hand. The ending “-ment” is from the old English word mund, hand. The shaftment was an important unit in Saxon England, where it was equal to about 16.5 centimeters (6.5 inches). After the modern foot came into use in the twelfth century, the shaftment was reinterpreted as exactly 1/2 foot or 6 inches (15.24 centimeters).