It has never been ambiguous. : refers to a ratio. Not necassarily a percentage. For every x: part in the final formula there are :x parts for it to be added to. And a ratio in the spoken language is pronounced- to. So 1:3 is pronounced and meant to be 1 part of something added "to" 3 parts of something else. It turns out to be a 25% dilution but that is secondary to what the ratio is. Not ambiguous at all. Pretty simple. James(posted 8475 days ago)