How to keep a hair color formula log for repeat clients

Hair color gets much easier when the formula log is written like another stylist may need to use it tomorrow. I used to keep short notes that made sense only to me: level 6 warm brown, toner mixed cool, processed 30. That sounds fine until the client returns eight weeks later, the lighting is different, the ends are faded, and nobody remembers exactly what happened. Now I write the starting point…