Best way to store timezone offset?

I want to store timezone offset data along with my metric data - so I can show data in local time when necessary. Timezone offset won’t change very often - for most series, probably twice a year. I don’t need to ever lookup or filter by offset - so there is no need for it to be a tag. Would this work best as a field (to reduce cardinality) or a tag (to reduce the amount of data stored)?

@David_Price I think this would work best as a field. That data (almost always the same value) will compress down to almost nothing. And RAM (for tags) is more expensive than disk (for fields)