w/v, weight to volume. A ratio of the weight of dry raw material per volume of extracting fluid, expressed in grams per mL or kg per L. For example, 1:10 w/v implies that one gram of dry allergenic material (e.g. pollen) was extracted in 10 mL of extracting solution. A 1:20 w/v extract is half the concentration of a 1:10 w/v extract, since the same amount of allergenic source material was extracted in twice the volume of extracting solution. w/v designation is used as a rough gauge of potency in non-standardized extracts.