Talking, I'd say 'a thousandth' or 'a tenth of the %'. Applying 'a' as an alternative to 'just one' in stating it seems nicer. Further more, in exposition, 'a' is surely an indefinite short article, which indicates the speaker does not know the id from the noun, In cases like https://kameronlhbzp.suomiblog.com/not-known-details-about-thca-flower-wholesale-52238351