Why does a 1.75 oz/50 g ball not always weigh exactly 1.75 oz./50 g?
If you weigh a ball of yarn, you may discover that not every ball weighs exactly 1.75 oz or 3.5 oz/50 g or 100 g. This weight difference for individual balls can have various reasons; a certain amount of deviation is legally permissible. Wool, in particular, is well-known for its moisture-retaining ability. A wool fiber can absorb moisture up to a third of its dry weight without feeling damp. When placed in a dry environment, the moisture is released again. Each fiber has an international, legally established moisture regain. The legal moisture regain for REGIA, with a blend of 75 % virgin wool and 25 % polyamide, is 15.25 % of the oven dry weight of the yarn. In heated and dry rooms, articles with a high percentage of wool loose moisture, and therefore weight, so the weight of individual yarn balls changes. Of course, the length of the yarn is not affected.
As far as REGIA is concerned, the weight - without wrapper - of a 3.5 oz ball or 1.75 oz ball may legally vary by as much as 6%. Since the weight of a ball of yarn may vary, depending on moisture content, the amount given on the wrapper may include the qualifier "conditioned" or two tildes, one over the other (≈), which means "is approximately equal to" in the relation of length per given weight. Packaging laws require that yarn balls be labelled according to weight but during production balls are measured by length.
If during production the machine which makes the yarn balls is not set correctly, e.g. if the yarn tension is too high, it can happen that the yarn in a ball does not have the correct length. This generally results in a weight below the legal tolerance limit and such a ball is no longer sufficient, for example, for one sock. This is a production error about which, of course, a complaint can be registered.