marked up level

It seems to me that having multiple vials in the same orientation is redundant, but many levels seems to include this feature. What am I missing? There has to be some reason.

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    Most I have seen have the second end vial at 45 degrees. – Someone Somewhere Oct 11 '18 at 6:40
  • In my Contractor Level both vials are adjustable. I can precisely turn them and set up any direction I need. I didn't even know my level is adjustable and I used it a while before my friend showed me how to calibrate it. :) – Sergey Oct 12 '18 at 11:37

It's useful when using the level in the vertical direction (to e.g., check studs for plumb-ness) so that the bubble is at or near eye level no matter which end is up.

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    Yep. It would be annoying as heck to find oneself looking at a blank level beam 50% of the time. – isherwood Oct 10 '18 at 17:35
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    It's always satisfying when the technical reason (as described in user20637's answer) and the user-interface reason (as described in yours) line up perfectly. – David Richerby Oct 11 '18 at 12:55
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    @DavidRicherby Of course they line up perfectly, we are talking about using a level! – manassehkatz Oct 11 '18 at 15:33
  • This is the right answer. If you have a 4' level do you want to squat everytime you are putting up a vertical on a wall? In fact my 4' level has three. – DMoore Oct 11 '18 at 18:41
  • Interesting. My Dad always told me this was because you could not be sure that one edge of the level was square. He taught me to always measure one way, flip the level and measure again. Only if both measurements were the same could I be assured of plumbness. – Michael J. Oct 12 '18 at 21:38

For a spirit level to work the tube cannot be perfectly straight and of constant diameter. For the bubble to float towards the middle either the tube curves up towards the middle (a "block vial") or it has greater diameter towards the middle (a "barrel vial"). If it is curved up towards the middle - the cheapest alternative - it won't work upside down. In levels such as your picture the tubes at either end curve in opposite directions, so that the upper one works.

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    While this sounds like a good explanation, both vials on the level I have on hand work in both orientations. – DaggerOfMesogrecia Oct 11 '18 at 13:52
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  • From that same article, we can see that this tubular level does not have such a curve. – T.J. Crowder Oct 12 '18 at 12:32
  • Minimum curve is still required, even if it is unnoticeable to the eye. Otherwise bubble would have no "motivation" to rest right in the middle and would happily rest on any point along the straight surface. Another point - in cheaper levels barrel shape could be somewhat uneven, so when placing vial into the level manufacturer would simply rotate it "best side up". P.S. And yes, I was mistaken once to use cheaper level upside-down - was off my ~1.5cm over 2m span. – Kromster Oct 15 '18 at 4:25

Contractor-grade levels are expensive, compared to home-grade levels.

Whether that premium cost is justified by build quality or not is a separate topic.

So one way to distinguish the more-expensive ones is to have more visible features/accessories like multiple sight vials.

A lesser second advantage is redundancy - a finely made level becomes nothing more than a fat straight-edge if its vials are broken or become inaccurate. With multiple, you can keep working and continue to use the tool, rather than halting work (which means progress and income stops)

The best tools are those that keep working, so you can keep working.

  • This is in addition to the other answers, but was too long for a comment. – Criggie Oct 12 '18 at 21:26

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