Pound (mass) for the weight of certain precious metals, especially in the trade; these are normally quoted just in ounces (e.g. "500 ounces") and, when the type of ounce is not explicitly stated, the troy system is assumed. Historically, the pound sterling was a Tower pound of silver. In 1528, the standard was changed to the Troy pound. The avoirdupois pound, also known as the wool pound, first came into general use c. 1300. It was initially equal to 6992 troy grains. The pound avoirdupois was divided into 16 ounces. During the reign of Queen Elizabeth, the avoirdupois pound was redefined as
Canal pound called these "mule drinks", since the mules would drink from the water flowing over the towpath. Informal overflows were often replaced by a waste weir or lined with concrete or masonry to make a more "permanent" spillway. If the pound was many miles long, sometimes the canal would be designed with stop gates, so that if there was a break in the canal the whole pound would not lose all its water. Isolating the break would allow the company to make repairs sooner. For instance, on the 14 mile level of the Chesapeake and Ohio canal, there were stop gates