No, it is accurate to 1/4 inch over 300 feet, and 1/4 inch accurate over the next 300 feet

Only if you perfectly align it.

If there is any uncertainty/error in the alignment, then that will impact the uncertainty as well.

It WOULD be perfectly aligned, same as everything ELSE would be.

Laser levels would be almost useless, if they couldn't be perfectly aligned, or 'plumb', or 'square', before anything is measured with them! That's rather obvious, isn't it?

You seem to think we cannot measure any surface accurately, when it is 'too long', whatever that's supposed to mean!

I'll try to explain why you're wrong, that they CAN measure for 'curvature', which you say is so incredibly 'slight' of a curve, over the Earth, that we cannot measure it, over a 'small' distance, which is any distance we CAN, and HAVE, measured!

The laser level is aligned, or squared, precisely, beforehand. It's height above sea level, or 0 feet altitude, is also set.

300 ft is 3600 inches, or 14400 quarter inches. The maximum error over that distance is 1/4 inch, when in perfect alignment, and would be, so it's accurate to 1/14400 unit over that distance, or 0.0000694 maximum variance. This gives you an idea of how accurate it is, without a doubt.

But here's the best part - even though it ISN'T perfectly accurate, being out by a tiny fraction like this, what we CAN do, and WOULD do, is measure within that 300 foot distance, to find out it is still perfectly aligned, or square, and measure the HEIGHT above sea level, at each point.

Or we can simply use shorter distances, with the laser level, which would make it more accurate, over each measurement, that also would work.

I'm trying to explain to you, that we absolutely CAN measure a surface as being flat, or curved, over a one mile distance, or more, with absolute accuracy, that is a fact. It may not be spoken of, may not be claimed as a fact, and they never do, in public, at least. But they certainly KNOW it is a fact, and some have actually MEASURED it, proving that it IS a fact.

With laser levels of today, almost anyone can do it.

You're suggesting 'curvature' is too slight over 300 feet distance, because it has a 1/4 inch variance, which is less than 'curvature' is, over that same 300 foot distance.

So how did they know, when testing their laser level, that it actually WAS, at very most, inaccurate, over a distance of 300 feet, BY 1/4 inch?

Because that's the most important part you need to know about here.

They couldn't have known it was off by 1/4 inch at most, over 300 plus feet, unless they had MEASURED the CORRECT point, from 300 feet away!

Since you haven't disputed that figure, I assume you accept it as true, and we can move on...

Obviously, they couldn't know it was off by 1/4 inch, at most, unless they knew what WAS the correct point, from 300 feet away, or actually 324-5 feet away, or whatever it is, but they must have found out, it becomes less accurate at any LONGER distances, by measuring for the correct point there, as well.

And, if they have measured the correct point, where the laser level WOULD always hit, from 300 feet away, then obviously, we CAN measure it accurately, and HAVE measured it accurately, over a distance of 300 plus feet.

If THEY measured it, anyone else can measure it, too, the same way they did.

We know, they certainly knew, that a laser light is a perfectly straight line of light, so when they tested it for accuracy over 300 feet, or every 10 feet further out, or whatever, they had to set their targets at the exact same height, over all of the targets, at all distances outward from the laser level.

They had to set the targets at the exact same height, to a micron, or whatever is going to establish maximum accuracy.

When they measured a target at 300 or 400 feet away, they must have known the target point had to be at the EXACT SAME height as the laser light was, 300 feet way from it. They had to know it's exact direction, to set their target in the exact direction of the laser light, 300 feet away, at each side of it, too.

They set up targets at specific distances away from the laser level, with points on each target, set at the exact same height, exact same line of direction, as the laser level.

Why couldn't they have set the targets for 'curvature'? Because if they wanted to, each target would be set lower, to curvature from the laser level, to the targets, which would lower more and more, with each target further away, to match up with it.

To measure a point on a target, at 300 away from a laser level, means we can measure points on targets over any distance, because they never account for this completely made up 'curvature' of the Earth's surface.