# Digital level opinions

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#### Little Scrapper

##### Well-Known Member
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Alright, now for us basic shop guys I just ran a simple test to see if the average person could set the level to calibrate it using basic tools.

I set my Costco plastic membership card under one side of the level.

The card is about .020" I suspect. The digital readout measured .10 degree.

What I really wanted to see was if my wife could see the difference in the bubble and sure enough, she said she could easily tell the bubble was shifted to the right, or the side of the card etc.

It was drastic enough that I took a picture of the bubble with my cell phone. I tried to center the phone over the lines and it turned out pretty good, can you see how it's shifted off of center?

Again, that just goes to show how accurate the human eye actually is....and my eyes are not the best. Lol.

Well, I guess that's enough, you get the idea I'm sure.

Scrap

#### Midniteoyl

##### Well-Known Member
Stabila has some of the most accurate spirit levels.. Using the $40-$90 big box store levels wouldn't have shown such a difference.

Glad you like the level and thanks for the review

#### Little Scrapper

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Likewise Jim, thanks for the suggestion as well as the link. It was a great deal!

#### ekimneirbo

##### Banned
Ok. So the manager met me at the machine shop and fortunately a young machinist with some really wicked tools decided to hang out with us before going home and we borrowed his tools. A couple things I learned about this.....

It's easy to get caught up in to numbers game because the Stabila level itself has graduations that measure .01 degrees at a time, definitely fine from a builders perspective but when comparing against real machinist tools hardly accurate at all. The first thing we did was set it on a very flat surface plate that's insanely accurate and checked for accuracy frequently given the nature of the business they are in.

I learned that machinists have various types of tools in which to measure angles, I was quite surprised really, very interesting tools them guys use. Anyhow, we zeroed or calibrated the level on the plate and set it to zero degrees. Once that was done the "Brad" the young machinist, decided it was smart to take off the 2 rubber ends on each end of the level so the level was measured on just the aluminum extrusion itself. We then put the level on a massive steel adjustable angle thing that measure about 12" X 12" square. He set it by eye than put a machinist level on it and dialed it in. He said his machinist level was accurate to .0005" , or 1/2 a thousandth in 1 foot. The machinist level I would say was less than 20". Regardless, the angle plate thing he set at exactly 10 degrees and when the stabila level was put on it is registered at exactly at 10 degrees. So far so good.

We then shut the level off, shook it, twirled it, and checked it again. Exactly 10 degrees.

We then left the level on and shook it, twirled it, and checked it again. Exactly 10 degrees.

Interestingly, when we set the angle at at exactly 45 degrees the Stabila was off by .05 degrees, bounced to .00 and then settled at .05 degree. We went back to the surface plate and checked it again, dead nuts at zero degrees. We did a few other things and basically came to the conclusion the anything under 30 degrees from level or plumb the Stabila is absolutely dead nuts accurate. but for some reason right around the 45 degree mark it tends to be off a hair. This really means nothing to me because .05 degree on a 45 is irrelevant to what we are dong with airplanes.

Everything above is pretty irrelevant though because in a shop like you and I have to build these airplanes in we simply don't have access to an accurate surface plate. So I guess the real test is NOT on a surface plate but rather buy eye, so that's what I did. In the machine shop Brad had his tool box shut so I set it on top and shimmed it by eye until the spirit vial was level or at least according to my eye it seemed level. Once I was happy I zeroed the level and calibrated it from the bubble. Brad then took his machinist level and set it on top of the Stabila. I was really shocked, blown away actually, just by eye I was able to level the bubble to dam near .010". I would say his tool box that I set my level on was about 30" long as far as the surface is concerned.

Here is what I learned. First of all I love the level, the build quality is typical of the Germans, solid as a rock. Second, there's no need for a digital level if you just need things level and plumb because the naked eye...assuming you have a very good quality spirit level, is freakishly accurate. I can literally calibrate the level by eye and be confident it's level. I'm glad I bought the digital level because I can set angles with it.

The Stabila level I bought has all sorts of features that I probably will never use. I do like how well the back lighting works and how you can read the numbers form the side or the top.

So that's that. I love it!

Scrap
That was an excellent review that you posted. Your conclusions reflect what I tried to say earlier....that we are expecting too much to think that we can work in a few thousandths of an inch and project that for any distance beyond the length of the level. When stacked up against true machinist quality equipment you can see the difference, but even the true machinist level has limits for what we want to do...initially flat and level for 16-20 feet for a table. What you were able to do was explain the fallacy that we all tend to fall for.....that because we are looking at a digital readout, what we are seeing is as perfect as we can get......when the reality of it is that stepped readings with actual numbers are less precise than gradual visual reference like a bubble. Now even that goes back to whether the instrument
(level) of our choice is accurate to begin with.....but we can see gradual movement of a bubble sooner than we can transition one decimal point on a readout. We didn't have any idea how much this movement of a bubble actually represented before you researched it (at least I didn't). Now we have some idea of how much movement is required, and know that reading it on a digital scale doesn't
necessarily mean its more accurate....but used properly they both can provide us with good information.Remember that also applies to using a digital caliper.

Once we move beyond the table and get into the building stage, a bubble level will work just fine for any two things we want to be level, or a small level surface. Leveling wings, thats another matter that I believe is best done with a water level, then compared with a digital (angle finder) level. Checking angles is where the digital level (nee angle finder) really outshines the bubble level. I am adding some pictures of one more level that I acquired quite a while back.
The bubble is much larger and flatter with graduations. As far as I know, this coup de grace for leveling something by hand.

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#### Little Scrapper

##### Well-Known Member
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I thought the Stabila was extremely accurate. There's no way I'd buy any other brand of digital level. The bubble is what makes it accurate. The levels from menards, home depot or Sears are no comparison to a Stabila. I don't mean just digital, I'm talking about the spirit bubble part.

#### TFF

##### Well-Known Member
A buddy and I put up his plane and were walking around the airport. We saw a hangar open that had a just almost finished finished Pitts M-12 in it. We asked to look a round The owner was trying to set one of the flying wires the way the M-12 instructions have you do it; you essentially tighten the wires to the right dihedral and they are set. He was calling out numbers like 8 then 5 then back to 8 then back to 5. Everybody though wow 3 degree variances, thats messed up. He was calling out the tenths. "Unless you want to buy a handful of flying wires to get the closest measurement, let it go, " said his buddy. The plane won best something at Sun in Fun that year.

#### ekimneirbo

##### Banned
For anyone who has a digital level and wants to check its accuracy.....we all know about putting a level on something.....getting a reading......and then switching it end for end to see if we get the same reading.

If you have a digital level and want to check it, do the same thing on a part that has a known angle like a roofers square. The level should read the correct angle and read the same when turned end for end.

Don't freak out if it varies a 1/10, its still plenty accurate for our needs when used properly.

True story: Machinists and inspectors don't always get the same readings either. I was machining some aluminum castings that had four precision holes thru them. The holes had a 2/10,000 tolerance (henceforth
referred to as 2/10ths in machinist lingo. The holes did not need to be that precise, as their only function was to have a pin pressed into them. As most people know, you usually have 1 or 2 thousandths of interference
when pressing a pin into something. So we were holding the holes to a much closer tolerance than needed. Two of the holes were 4 inches long to go all the way thru the part, and the other two holes only needed to
be two inches deep to also pass all the way thru the part. Oil based coolant was sprayed liberally on the part and reamer as the part was finished to size. The same reamer was used to finish all 4 holes. The reamer worked
just beautifully in all 4 holes except the last half inch of depth on the 4 inch long holes. There it began to go under the tolerance by 1/10,000 of an inch. It would have absolutely no effect on pressing the pin in the hole, and there was no way to adjust it, because it didn't do it every time. At this point I should mention that measurements by different people aren't always the same, but measurements by the SAME person are not always the same either.
After pleading my case to the inspector, he refused to accept the part and "wrote it up". Realizing how rediculous he was being, I waited two days and then resubmitted the same part for inspection. This time he gave it
a clean bill of health. Upon receiving the new inspection record I returned to the inspection station with the part and both inspection records in hand. The inspector accused me of substituting another part. I told him to
check it out and see for himself. He spent quite a bit of time trying to find some previously machined dimension that didn't match the record, but finally had to admit that it was in fact the same part he had written up 2
days earlier. I told him that my point was not to embarass him but to get him to be realistic about not only the ability of a machinist to hold some excessively close tolerances, but the ability to verify those tolerances
"perfectly". There is a little to be said for feel and finese when inspecting parts. I later spent about 5 years as a machined parts inspector, using computer controlled Cordinate Measuring Machines and even spent some
time as a gear inspector. I only say that because I feel that having machined and inspected thousands of precision components, I'm familiar with variation in the readings obtained by different people using both the same
inspection tools and even cross checking with different tools. I don't care how precise the tools are, there will be variation. I also spent time as an inspector in the fabrication shop, so I'm familiar with how many fab
components vary in manufacturing....and some fab components also have tight tolerances...like the prepunched holes in an RV kit. The bottom line to me is that builders don't need to fret about absolute accuracy, because
its basically unobtainable in scratch building an airplane....but be diligent about at least trying your best to be as accurate as is reasonable. Again, Thanks to Little Scrapper for making this thread and doing the legwork!

#### Aerowerx

##### Well-Known Member
I have a neat free app on my smart phone that displays angles in two directions simultaneously. The display is to 0.1 degrees. The computer desk I am sitting on is, for example, level in the east-west direction but 0.3 degrees off in the north south direction.

The name of it is "Clinometer".

#### Midniteoyl

##### Well-Known Member
Not really the most accurate..

#### TFF

##### Well-Known Member
Maybe the Earth ,East-West, is off .3 deg.

#### PTAirco

##### Well-Known Member
For anyone who has a digital level and wants to check its accuracy.....we all know about putting a level on something.....getting a reading......and then switching it end for end to see if we get the same reading.

If you have a digital level and want to check it, do the same thing on a part that has a known angle like a roofers square. The level should read the correct angle and read the same when turned end for end.

Don't freak out if it varies a 1/10, its still plenty accurate for our needs when used properly.

View attachment 47378

True story: Machinists and inspectors don't always get the same readings either. I was machining some aluminum castings that had four precision holes thru them. The holes had a 2/10,000 tolerance (henceforth
referred to as 2/10ths in machinist lingo. The holes did not need to be that precise, as their only function was to have a pin pressed into them. As most people know, you usually have 1 or 2 thousandths of interference
when pressing a pin into something. So we were holding the holes to a much closer tolerance than needed. Two of the holes were 4 inches long to go all the way thru the part, and the other two holes only needed to
be two inches deep to also pass all the way thru the part. Oil based coolant was sprayed liberally on the part and reamer as the part was finished to size. The same reamer was used to finish all 4 holes. The reamer worked
just beautifully in all 4 holes except the last half inch of depth on the 4 inch long holes. There it began to go under the tolerance by 1/10,000 of an inch. It would have absolutely no effect on pressing the pin in the hole, and there was no way to adjust it, because it didn't do it every time. At this point I should mention that measurements by different people aren't always the same, but measurements by the SAME person are not always the same either.

Exactly. Unless you use the same tool all the time, in exactly the same way and are used to it, another person will never get the same reading. Which is why in the old days, production shops used go-no go gauges as much as possible. If I measure a part with a micrometer, I probably do it a dozen times and then take an average and call it good enough. With homebuilt airplanes, anything more is pointless overkill.

#### ekimneirbo

##### Banned
There is one more thought I would like to mention. No matter what level you are using, the bubble will always seek out the highest point. If the vial holding the bubble is installed correctly
the reading will always be correct unless the builder has overlooked something like dirt or grit. The things which can be done to create more accuracy after you have established the
basic orientation of the vial/bubble are the use of different fluids and/or a flatter (larger radius) vial. A longer vial with almost a flat arc will be more sensitive to minute angular variation. For
the most part levels use similar size and shape vials , and have main bodies which are very parallel and accurate. Use your calipers and check the body of your level in several places and you
probably won't see a .001/.002 of variation. That is something the bubble will never notice. So really, in most construction type levels...if the vial is installed correctly the accuracy will be there.
You can look at the amount of radius various manufacturers use to see if there is any noticeable difference, but for the most part they all use short vials and a similar radius.

Quality and durability is a completely different matter.....and I think that is where added costs come into play. Along with that added cost is most likely some additional verification that the vial
holder is held to an exacting location. The occasional misplaced vial is less likely to happen......but common sense tells you that manufacturers putting out thousands of levels in a production run
are going to make some pretty decent ones even if a few slightly less accurate ones find their way to market. I mean, you have to ask yourself why a manufacturer would design and produce a
tool that was built for one specific purpose.....and then produce one that was inaccurate as a normal course of production. Personally I think many times the levels get blamed for the mistakes
of the users. So I agree that a quality level will be better designed and made...and should always be accurate when purchased.....I also feel that inexpensive levels often get an undeserved bad
rap.

A friend stopped by the other day and was having issues with his chop saw. He went and bought a new one ....a quality name brand unit. When he made his first cuts, they were out of square
vertically. He is pretty handy at building things. He took the saw back and they gave him a replacement. He took it home and had the same problem. He called the factory and after some discussion
they purportedly admitted they had a production run that produced some bad chop saws. He returned the chop saw again and went to a different retailer and bought a different brand. As far as I
know, that solved his problem............or he found out that something he was doing caused it and corrected it. I haven't talked to him since then, so I don't know. The point I want to make is that
the brand he bought is a top name brand with a good reputation among trades people. What was the real cause of the problem...him or the ocassional factory hiccup.........

Here is what Wikipedia has to say:
Sensitivity
The sensitivity is an important specification for a spirit level; its accuracy depends on its sensitivity. The sensitivity of a level is given as the change of angle or gradient required to move the bubble by unit distance. If the bubble housing has graduated divisions then the sensitivity is the angle or gradient change that moves the bubble by one of these divisions. 2 mm (0.079 in) is the usual spacing for graduations; on a surveyor's level the bubble will move 2 mm when the vial is tilted about 0.005 degree. For a precision machinist level with 2mm divisions, when the vial is tilted 5 arc seconds the bubble will move one graduation. This is equivalent to movement of .0005 inches measured one foot from the pivot point; referred to as 5 ten thousands per foot.

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#### Aerowerx

##### Well-Known Member
Not really the most accurate..
Can you support that statement with documentation?

It probably uses the same type of MEMS sensors that are in the digital readout levels. Just because it is in a smart phone wouldn't make it worse than any other digital level.

Besides, there is a calibration procedure that you have to run on it that removes most of the residual errors in the MEMS sensors. Do you do that on the digital levels?

#### Aerowerx

##### Well-Known Member
Maybe the Earth ,East-West, is off .3 deg.
Nonsense.

The definition of "Level" is "perpendicular to the local gravity vector". What ever that gravity vector is, my computer table is off by 0.3 degrees. Considering it is a hand-made wood table sitting on a wood floor in a 60 year old house, 0.3 degrees isn't too bad.

Even if I was sitting on a playground slide, "level" is still level.

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#### TFF

##### Well-Known Member
Hmm, hum-mor I get it now.

#### Little Scrapper

##### Well-Known Member
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Given my.histogram smart phones I'd have a hard time trusting them.

#### Midniteoyl

##### Well-Known Member
Can you support that statement with documentation?

It probably uses the same type of MEMS sensors that are in the digital readout levels. Just because it is in a smart phone wouldn't make it worse than any other digital level.

Besides, there is a calibration procedure that you have to run on it that removes most of the residual errors in the MEMS sensors. Do you do that on the digital levels?
Because your phone and case are not held to any tolerances, with most having slight curves... thats why.

#### ekimneirbo

##### Banned

I guess I can understand now why the pre-eminent cartoon relating to plumbers is always the one about them showing their A**

Thats humor....if you were wondering.:roll:

Why don't we just limit our posts to factual and technical information that someone might find useful ?

#### Little Scrapper

##### Well-Known Member
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My azz crack makes me a lot of money. That's humor.

Seriously. It's beat to death.

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