If you look at a long level there are usually two "bubbles", side by side ... one concave up and the other concave down. I have always read the one that is concave up in any application. No one at Home Depot or Lowes home improvement stores seems to know the difference. Would you please explain the difference, and which to use?
Thanks for your input,
Bob Burkett snipped-for-privacy@verizon.net