I just wanted to point out that it is confusing to have
US = 'en_US'
METRIC = 'en_UK'
because the only reason 'en_UK' gets you metric is because it is an incorrect form of what I'd assume is supposed to be 'en_GB', the language tag for British English. Also, this is confusing because the 'en_GB' tag isn't metric but British (so it uses stones, for example).
I just wanted to point out that it is confusing to have
US = 'en_US' METRIC = 'en_UK'
because the only reason 'en_UK' gets you metric is because it is an incorrect form of what I'd assume is supposed to be 'en_GB', the language tag for British English. Also, this is confusing because the 'en_GB' tag isn't metric but British (so it uses stones, for example).
See here: https://dev.fitbit.com/build/reference/web-api/basics/#units