I'd agree with Tim. They're an interesting tool, but the color level per se doesn't convey a lot of information. I've been pretty much getting readings for the whole 7 weeks I've been on induction. Sometimes they barely turn color, but they do change slightly, and occasionally they read out a moderate change, but rarely darker than moderate. I've virtually NEVER had deep purple reading. I think your hydrations levels influence how much the ketones are diluted or not and that in turn reflects on the color change on the stix. They are mildly interesting...not much more. Just one tool out of many. I enjoy using them, but don't take it all that seriously.