Imperial and US customary measurement systems different concepts – the imperial gallon is defined in terms of the volume occupied by a specified mass of water, while the US gallon is specified in terms of cubic linear measure. Notes Notes Units of weight in both the imperial and US customary system always used the same standard, though differences in multiples of the avoirdupois pound developed in the nineteenth century. Both systems used the three different scales – the avoirdupois system for general use, the troy system for precious metals and the apothecaries system in the pharmacy industry. The term "weight" and "mass" are used interchangeably in
Yarn weight Yarn weight Yarn weight refers to the thickness of yarn used by knitters, weavers, crocheters and other fiber artists. Changing yarn weight or needle size can have a significant impact on the finished project, so standardized systems have been spread about, as well as conversion systems for regional standards (especially needle sizes). Yarn weight is important in achieving the correct gauge or tension for a particular project and can help with yarn substitution. The Craft Yarn Council of America has developed a system that seeks to standardize the labeled weights of yarn. Most yarns state their weight on the ball