@cheddar and @kentquirk I know you all and I discussed this before, although I'm unable to find the discussion now (after searching issues somewhat lackadaisically). As will not be a surprise, I do agree with @jh-bate on this issue. I'm willing to compromise as long as we're preserving the string value of the original datum, but I would then want to include validating this string value against the converted value given to tideline as part of tideline's validation step (that we've discussed here https://github.com/tidepool-org/tideline/pull/111, although validating the equality of the string values and converted values would not be something that could be included in the schema).

In specific response to some of the comments here:
> The fact of the matter is that 100 and 101 are not very different. Same with 45 and 46 (you're gonna be treating for either of them) as well as 201 and 202.

I don't believe the "not very different"-ness of 100 and 101 mg/dL is at all relevant to the issue here. The issue is not what Tidepool's users are doing with the data we provide for them (treating or not treating, etc.); the issue is our role as stewards of patient data and whether stakeholders (patients/caregivers/doctors/researchers) can *trust* us with data. I wouldn't trust a platform that gave me back a 101 mg/dL when I put in a 100 mg/dL (only an example, not claiming this is a likely scenario given the proposed implementation).

I'm also not convinced by the assertions being made for storing values in one unit:
> We should NOT store numbers as entered as numbers, and the database should not have two different types of readings in it. That way lies madness.

I would like to understand more of what's motivating this assertion, as well as real-life examples. What, for example, does the T1D Exchange do? What do international research groups do? I do know that even U.S. researchers use `mmol/L` in their published studies because that is the accepted international standard; that is a potentially good point in defense of storing in `mmol/L`. Let's both do our due diligence here and avoid reinventing the wheel by trying to find out what the best practices are in this particular realm, if any currently exist.