Thanks, cruciverbalist. Those were tough to rationalize, and poorly phrased clues.
30D - finally see the A - "are" - metric unit.
24D - "out of base" is just bad wording. Considered "E", but for the longest time thought it was a triple def. & had "ONCE", ie "on a single occasion" & "in the past", so the first part made no sense.
Doc needs to do some better editing.