So, a Starrett 98 6" level walks into a bar...

Interesting videos.

I wonder about his technique, though. He fixed the level's position and repeatedly adjusted the level.

I'd imagine it could be more efficient, at least at the start, to adjust only the position of the level until swapping sides does not move the bubble, without actually adjusting the level. After that, you would in principle only need to adjust the level once, to put the bubble in the middle.

Both sides of mine arrived loose and almost entirely unscrewed. How tight should both sides be?
 
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I think you have misunderstood what is going on when you adjust the level. A level is properly adjusted when readings are the same when it is flipped 180 degrees. This tells us that the bubble vial is parallel to the base it is mounted on. A level that reads x number of divisions off, then is flipped and again reads the same x number of divisions, is properly adjusted. You don't need to have the bubble centered when adjusting, people just do that because it is easier to keep track of where you want to adjust it to, instead of having to remember something like 4 1/2 divisions to the left.
 
hudstr said:
I think you have misunderstood what is going on when you adjust the level. A level is properly adjusted when readings are the same when it is flipped 180 degrees. This tells us that the bubble vial is parallel to the base it is mounted on. A level that reads x number of divisions off, then is flipped and again reads the same x number of divisions, is properly adjusted. You don't need to have the bubble centered when adjusting, people just do that because it is easier to keep track of where you want to adjust it to, instead of having to remember something like 4 1/2 divisions to the left.
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Thanks, but I do understand that. I was commenting on the difference between changing the position of the level until it finds a genuinely level part of the surface and adjusting it once, vs. placing it anywhere and adjusting every time the ends are swapped. (Every flat surface, including those that are not parallel to the ground, is level to the earth along some orientation.)

So, technique 1 (as in the video): Place the level anywhere (non-level) and fix that position. Swap it end to end while adjusting the level each time its swapped until the readings are the same. You now have a calibrated level despite the fact that the bubble is not visibly centered. Then the level, if placed on a genuinely level surface, should have a centered bubble.

Technique 2: Place the level on any flat surface and swap it end to end. To the extent that the readings don't match (which it won't at first), change the orientation of the level along the surface. Turning it one way will make the readings converge, and the other way diverge. Converge on an orientation at which the readings are identical. You have now found a level position on the surface. Now just adjust the level to center the bubble. If you reverse it again the bubble should remain centered. The advantage of this technique is that you only adjust the level once, and you get the satisfaction of seeing the bubble centered.
 
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Huh, I'd never thought of Technique #2 before! That is interesting! I never knew that "every flat surface is level to the earth in some orientation" bit, but I think it conceptually makes sense to me.
 
zondar said:
Technique 2: Place the level on any flat surface and swap it end to end. To the extent that the readings don't match (which it won't at first), change the orientation of the level along the surface. Turning it one way will make the readings converge, and the other way diverge. Converge on an orientation at which the readings are identical. You have now found a level position on the surface. STOP HERE Now just adjust the level to center the bubble. If you reverse it again the bubble should remain centered. The advantage of this technique is that you only adjust the level once, and you get the satisfaction of seeing the bubble centered.
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That is correct until the 5th sentence, no adjustment is necessary. You can't move the bubble to the center by adjusting if the previous sentences are true, if flipping a level end for end shows the same reading. What this proves is that the the bubble vial is parallel to the base it is on, and that the surface the base is on isn't level (in that orientation). In this situation, you would just be able to keep rotating the orientation until you actually find a spot where the bubble shows the surface is level (with the bubble in the center), and to prove the bubble vial is parallel to the bottom of the level(by having the same reading 180 degrees apart).



Seems I misinterpreted your use of the word identical. What you are saying is both readings have the same value, but one is "positive" and the other is "negative". Then adjusting the bubble half of the discrepancy, aka to the center of the lines, and then you are done. I thought you mean identical as in the exact same.

tom lipton has a video that explains it better than I can.
 
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zondar said:
Thanks, but I do understand that. I was commenting on the difference between changing the position of the level until it finds a genuinely level part of the surface and adjusting it once, vs. placing it anywhere and adjusting every time the ends are swapped. (Every flat surface, including those that are not parallel to the ground, is level to the earth along some orientation.)

So, technique 1 (as in the video): Place the level anywhere (non-level) and fix that position. Swap it end to end while adjusting the level each time its swapped until the readings are the same. You now have a calibrated level despite the fact that the bubble is not visibly centered. Then the level, if placed on a genuinely level surface, should have a centered bubble.

Technique 2: Place the level on any flat surface and swap it end to end. To the extent that the readings don't match (which it won't at first), change the orientation of the level along the surface. Turning it one way will make the readings converge, and the other way diverge. Converge on an orientation at which the readings are identical. You have now found a level position on the surface. Now just adjust the level to center the bubble. If you reverse it again the bubble should remain centered. The advantage of this technique is that you only adjust the level once, and you get the satisfaction of seeing the bubble centered.
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Technique 2 makes perfect sense and is what I will use from now on. I do prefer to have the level on two supports though to rule out any flatness issues.
 
Tom Lipton is performing a "technique 1" calibration, at least at first. He started with what turned out to be an arbitrary position and keeps that position while adjusting the level over and over. He does move it once later, but just to find a second position that is closer to level, and then he proceeds with "technique 1" again.

I do stand by my assertion that the "technique 2" is correct and is a better way to do it. Perhaps I could have been more clear about what I meant by "identical" readings, maybe? I meant the same as what is done in the "technique 1" version. (Edit: Yes, "identical" except for the sign, so +X and -X, where X is identical)

I especially like that the "technique 2" version does end up with a centered bubble, because you found a level orientation, and which can be reversed again to prove itself. You don't get that with the "1" version, and just have to trust that you would have a centered bubble if it was on a level surface.

I also note that Lipton is making adjustments by turning the slotted screw rather than the pair of nuts. I've wondered about that, as a fine screw thread should be a more sensitive adjustment than a pair of clumsy nuts. Which does one actually use?
 
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zondar said:
Tom Lipton is performing a "technique 1" calibration, at least at first. He started with what turned out to be an arbitrary position and keeps that position while adjusting the level over and over. He does move it once later, but just to find a second position that is closer to level, and then he proceeds with "technique 1" again.

I do stand by my assertion that the "technique 2" is correct and is a better way to do it. (Perhaps I could have been more clear about what I meant by "identical" readings, maybe? I meant the same as what is done in the "technique 1" version.)

I especially like that the "technique 2" version does end up with a centered bubble, because you found a level orientation, and which can be reversed again to prove itself. You don't get that with the "1" version, and just have to trust that you would have a centered bubble if it was on a level surface.

I also note that Lipton is making adjustments by turning the slotted screw rather than the pair of nuts. I've wondered about that, as a fine screw thread should be a more sensitive adjustment than a pair of clumsy nuts. Which does one actually use?
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Finding that level line on the plane isn't that easy to do with an uncalibrated level. However, you can bound that approximate line with a poorer level. What makes it tricky is if your level (to be calibrated) is very sensitive. Then you have to find a levelish line on the plane whose slope is within the total number of divisions of that sensitive level. If that line exceeds that slope, then your level will always peg, no matter what you do. A pegged level won't calibrate.

Of course, if you already have a flat truly level surface, then you are golden. :) Many of us don't have a truly flat plane in their place. All of us may have that level line, but it isn't simple find it within the precision of a sensitive level. 5 degrees rotation from the level line, and you are well out of range, at least with a 0.02mm/m level. Less sensitive levels are easier to calibrate.

Have fun calibrating.
 
WobblyHand said:
Finding that level line on the plane isn't that easy to do with an uncalibrated level.

Have fun calibrating.
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You find the level line on a generally non-level surface with your uncalibrated level by rotating it until the bubble is +/- an equal amount from center when flipped. No need to know where that level line is before hand.

Of course, you do have to start with a flat surface that is at least somewhat level, or else your bubble will be out of range in most orientations. But with the 6" 98, this is not very hard (more sensitive levels are harder). It only takes a minute or so to get very close (I've tried it). After that, it's just a matter of how obsessive-compulsive the tool's owner is.

Also, checking the Starrett 98, the slotted screw thread cannot be used for adjustment. It just creates a pivot point. It probably shouldn't be screwed down too tight, either, as while that end of the level rests on a ball-shaped pivot, the bottom of the screw's head is flat. I'm still a little puzzled about this configuration. But on the 98, you apparently do have to use the nuts.
 
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