I’m still looking for a good answer where the pretty common convention of dropping the thousands originated. Been curious about that one for years. I suspect the abbreviation is a military carryover used for a number of things but that’s just a WAG.
I don’t use it, except when copying a clearance, but don’t get overexcited about it.
I don’t use it, except when copying a clearance, but don’t get overexcited about it.