Reading a "bubble Level"

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
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seniorgeezer wrote:

The two bubbles are for convenience. Use the one with the concave down for the position you are holding the level. You would use one if leveling something on the floor, the other if holding the level against something overhead.
Harry K
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Nonsense. You always use the one with the convex side up (or concave down, if you prefer), regardless of where you are taking your measurements. There are two vials so that you can use either side of the level. Makes no difference whether you're checking a floor or a ceiling, you *always* use the upper vial. The vials are slightly convex for two reasons: (1) so that the bubble will move slowly and gradually to the center as the level approaches level, and (2) to *keep* it centered. But this works only if you're using it properly: convex up.
--
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Doug Miller (alphageek at milmac dot com)
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Doug Miller wrote:

You're Right! I had to mentally picture it to see it.
Harry K
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air displaces the water & stays at the top of the tube. The highest point should always be up. hth Rob
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seniorgeezer writes:

A good level has a single vial that works either way. The concavity is bored into the inside of the tube.
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Richard J Kinch wrote:

You mean like my $10 orange plastic Home Depot level?
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The difference is that if you read the one concave up, like letter "U" then the bubble goes to one end or the other. Lifting or lowering an end of the level, and the bubble stays in the same place. [this is less useful]
If you read the one that is concave down (convex up) like the letter "n" then the bubble is in the center if the level is level. Or off to one side, if it's off level. [this is very useful]
Since you're reading the useless one, I presume people wonder why you're building crooked stuff all the time?
--

Christopher A. Young
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seniorgeezer wrote:

One is for use in the northern hemisphere and the other for use in the southern. Do _not_ confuse the two or you'll find your building is negatively level.
R
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RicodJour wrote:

Does this mean you need to read both vials on the Equator or at the Poles ??
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Reed wrote:

Now you're being silly. The Equator is essentially self-leveling since everything runs uphill from there. It might look different on a globe, but it's really at the bottom of a trough. The poles as expected are just the opposite - you just have to worry about plumb. If you don't believe me, just take a look at an Eskimo's igloo. That's what happens when you try to find level at one of the poles.
R
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On Wed, 28 Sep 2005 09:14:41 -0700, RicodJour wrote:

Nope. Antarctica is really on the bottom. Why do you think the ozone hole is there. It's all floated up to the top. You never hear of a ozone hole over Canuckistan!

It's easy to level one at the equator.
--
Keith


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wrote:

I guess then, on the equator you'd be out of luck & just do it by eye the way many framers do.
"plumb bob in one eye & a level in the other."
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seniorgeezer wrote:

I THEENK........
.:\\:/:. +-------------------+ .:\\:\\:/:/:. | PLEASE DO NOT | :.:\\:\\:/:/:.: | FEED THE TROLLS | :=.' - - '.=: | | '=(\\ 9 9 /)=' | Thank you, | ( (_) ) | Jeff | /`-vvv-'\\ +-------------------+ / \\ | | @@@ / /|,,,,,|\\ \\ | | @@@ /_// /^\\ \\\\_\\ @x@@x@ | | |/ WW( ( ) )WW \\||||/ | | \\| __\\,,\\ /,,/__ \\||/ | | | jgs (______Y______) /\\/\\/\\/\\/\\/\\/\\/\\//\\/\\\\/\\/\\/\\/\\/\\/\\/\\/\\/\\/\\/\\/\\/\\/\\/\\/\\/\\/\\/\\/\\/\\/\\
--
Jeffry Wisnia

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Jeff! Missed you!
--

Christopher A. Young
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