The ambigity of "dilution 1:3"

What is "dilution 1:3 " In medicine and chemistiry, dilulion 1:3 means dilute one part concentrate with solvent, such that the final volume is 3 part. In some photography formularies, however, "dilution 1:3" means dilute one part of concentrate with 3 part of water.

In the first case, the concentration is 1:3 or 33% In the later case, the concentration becomes 1:4, or 25% of original.

IMO, the usage in some photography writing ( dilute 1:3 as add 3 part water to 1 part stock ) is incorrect

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