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Totally rando thought - what is level?

And levels of all types also have their own inaccuracies.
 
Mike95060 said:
What are the criteria for “larger?” Mass? Area? Footprint? Height?

I love me some good mega project factoids :nerd
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Length. Longer projects like bridges, tunnels, highways… have to factor the earths curvature and will have a scale factor applied to horizontal measurements. Smaller stuff like buildings no matter how tall can assume the earth is flat and plane geometry is applied.
 
Scale factor. Interesting. So is that used to correct for the delta between the straight line distance and the chord of the arc distance when going to the same points?
 
It’s a factor applied to convert 2D geometry to spherical geometry such as going from a design created on a flat plane of paper or CAD screen to being constructed on the curved earths surface, which is actually represented mathematically as an ellipsis.
You can’t drape a flat 2D surface over the earth without distorting it. The scale factor accounts for that distortion.
It also accounts for the distortion caused by elevation. Same 2D design dimensions of something designed as if at sea level will have to be stretched if constructed at a higher elevation such as Denver because the spherical radius is greater being further from the center of the earth. So one best fit scale factor is applied to account for all corrections needed.

All covered under geodetics and geodesy.
 
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🤯
My industrial engineering curriculum required cross-discipline electives in thermodynamics, materials science, and electrical engineering. But nothing from civil engineering, which is where I’m guessing this would’ve been covered.

It makes perfect sense - just a concept I was never exposed to during my schooling, and never really came up since then. Love it. Thank you for explaining.
 
Clicked on thread expecting a philosophical discussion, instead, found a bunch of nerds flexing their critical thinking muscles.

Still interesting but now my brain hurts and I need to take a nap

I have a question though before I take a nap.... How did you mount the blinds?
 
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Sharxfan said:
Sometimes I just look at it and say "yup gud 'nuf for gubmint work" and walk away.
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In construction codes a .5" difference is allowable over a certain distance I can't remember but it's less than a large room. Found out the hard way installing a long shelf for a friend in her office. Holy gap batman.
 
When installing slabs for park tables, we used to say "everybody looks, nobody measures". This because you are often installing something next to something that is not itself square. So you make it as visually square as possible, and the hell with an exact measurement. Same with picture hanging.
 
Gravity varies from 9.77-9.83 m/s^2 on the surface of the Earth. Most of the diff is due to being further from the center of Earth mass on mountains at the equator compared to sea level at the poles. But some of the diff is due to high or low mass concentrations. Technically, being near but not on top of a high mass concentration will pull the gravity vector that way. The difference can be up to an arc-minute, 0.017deg. So everything built level in some places will lean a little one way.

 
Those tiny bubble levels on consumer grade (cheap) laser levels are notoriously inaccurate.
 
Mike95060 said:
What are the criteria for “larger?” Mass? Area? Footprint? Height?

I love me some good mega project factoids :nerd
Click to expand...
Slabs for buildings have tolerances built in that never require adjustment for curvature of the earth, because there aren't any long enough, but if there were one, they could form thicker around the perimeter to maintain a euclidean plane, kind of like embedding a square into the surface of a circle.
 
ThinkFast said:
So I’m messing around with my laser level to hang some blinds in our living room. The thing shoots this beautiful red line across the entire length of the wall. So I eyeball the alignment of the line to the window casement and then notice the casement has a slight slope on it. The bubble level on the side of the gadget confirms that I’m just a p.h. out of level, the casement sloping consistently about 2mm across a 16 foot span of windows.

And then I start thinking - and this is the (really) rando part - about our ride in the Outback in Australia when we lived there, and going to Silverton. On that road there’s slight rise in an otherwise dead flat desert expanse. So flat, in fact, that when you’re on this little rise in the road you can literally see the curvature of the earth. (This spot was used in a scene from Mad Max).

So there I was in my living room with my laser level thinking about that rise in the Outback and the earth curving and my 2mm drop, and I start wondering that maybe the 2mm drop isn’t really a drop at all. Maybe it’s just that my living room is following the curvature of the earth. And if that were true (ok, let’s just admit that it isn’t), then what is a straight line anyways? I mean, that line from laser was for sure dead straight. And the lines in my house are good and straight, too. Or are they? Maybe there’s no such thing as a straight line on earth because really they’re either all tangential, and therefore never square; or they’re all plumb and square, but they’re never straight.

They didn’t cover this very well in geometry - and I sucked at that anyways.

Ok - how’s that for random?
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Yeah, I mean, I used to see this all the time when I built things for a living. The problem you run into when using an independent source to level something inside the building is that often the building itself is not square the way you would like it to be.

You find the midpoint to tolerable to the naked eye and make due
 
Level ≠ perpendicular, but euclidean level = cum level.
 
When we put tile in our old house the tile guy would always tell me, “I hate level floors, I like flat floors.”
 
One way to check flat or level. To get extra nerdy check your shots by duplicating with one or more trackers.

This particular example units are millimetres (just as god intended) and both agree within 0.1mm, instrument accuracy 15 µm + 6 µm/m

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