I dont understand the point in using a level when someone is building something. That level may show that the floor, wall, or roof is completely level right now, but in an hour or day from now, it will no longer be level. The earth is rotating, gravity changes as the world turns, and what was level yesterday is not level today because of the earths rotation. After all, that bubble in the level is measuring whatever you're building, in relationship to the earths surface you are positioned on at that moment, and nothing more. This means nothing, because that piece of soil where you're working, will not be the same position in space in another hour.
When I build something, I do it all by sight. If I put a fence post in the ground, I can actually see it's off by as little as 1/4". If I measure that post from something like a house, I am nearly always accurate within 1/4". If I use a level, it almost always ends up being off by an inch or more, and I have several levels, and they are all accurate. That's if you want to call any level accutate, because none of them are accurate, simply because they are based on the present rotation of the earth.
It amazes me that in this age of high technology, we still use levels based on the surface of the earth, rather than having levels based on the entire solar system, the earth's position based on it's angle to the sun an other planets, and the plane of space that our solar system rides upon. Such a level would be operated by satellites in space sending signals similar to a GPS. It's measurements would be based on ALL the planets, not just the earth.
Yet, to date, we have nothing even close to this, and continue to build homes and skyscrapers based on outdated mathematic formulas which dictate the earth as a static object, which it is not. If we build a 1000foot tall building, it could at times be as much as 18 feet off of level at the top, in relationship the the our solar system and the universe. Of course this puts stress and strain on the foundation as well as the earth surrounding this structure, and results in eventual destruction of the building from within.
In a simple one or two story home, this is not noticable except for slight dips and sags in the floor. And most homes are built of wood, which tends to "float" and form according the position in relation to space. But these tall structures built of rigid materials such as steel and concrete, (including bridges), do not flex and are prone to disaster mostly because they are not of "TRUE level", that is level with the entire solar system.