Related Clues:
- See 57-Across
- 0, in some measures
- Where the buoys are
- The Caspian is just below it
- Part of New Orleans is below it
- Denver is way above it
- Mean position between tides
- Death Valley is below it
- Altitude baseline
- Where many geographical measurements begin
- 0 on an altimeter
- Land formation measuring standard
- Altitude is usually measured as height above . . . . . . . .
- Base from which height of aircraft is measured
- High over this has the ocean calm, it seems