Any thoughts on where to find "true level"?

[Gareth0123]

Get a tray of water big enough to fit the level in, put it in the freezer, wait for it to freeze, then without moving the tray you should have a flat surface.

Water expands as it freeze and that expansion could be off level.

 

[Gareth0123]

Is there a local Ordnance Survey Trig point (not a bench mark). The top of trig points are calibrated level and checked by O/S perodically

 

[Shox Dr]

Is there a local Ordnance Survey Trig point, not a bench mark. The top of trig points are calibrated level and checked by O/S perodically

Are they? They are at a ‘known’ height from sea level, and the top will be somewhat level, but certainly not level enough for this purpose. Main use is distance and angles using a Theodolite

Moot point as they are no longer used.

 

[DAPPH]

You could also use two simple electronic circuits , one in each end of a water gauge , juggle so one end is flickering then when the second one is also lit in a similar manner you will have found almost perfect level ( magnetic variances will have some effect on the levels too )

 

[Gareth0123]

About 30 years ago I watched the OS check a trig point, they even invited me to have a look see and then told me the level they were using cost well over £5K and had it's calibration check twice annually. I was quite surprised when they told me it was not recalibrated at Greenwich but at the British Geological Survey offices near Keyworth: about 15 miles from where I lived a the time

The level had a magnified reflector Vernier spirt level. You placed the level on the surface, flicked up the magnified reflector lined up the cross hairs and then read the bubble against the now magnified Vernier lines.

 

[zx9]

Well, I've learned loads from this thread so I'm happy

Happy is good, now what exactly were you trying to level? Please don't say a shelf and you ended up using your iPhone.

 

[Screwdriver]

You could also use two simple electronic circuits , one in each end of a water gauge , juggle so one end is flickering then when the second one is also lit in a similar manner you will have found almost perfect level ( magnetic variances will have some effect on the levels too )

...and you would have established that water is indeed flat.

Err, then what? Transfer a line with a pencil? Fit it with a laser beam?

I strongly suggest if anyone's that interested in metrology, subscribe to oxtools channel on YouTube. A decent machine level would have a fit and probably zoom off the scale if one end was half a pencil line higher than the other. There is a law of diminishing returns for calibrating any piece of equipment and the easiest, most effective way to set it up to within it's own tolerance is to use it to calibrate itself.

 

[Screwdriver]

Happy is good, now what exactly were you trying to level? Please don't say a shelf and you ended up using your iPhone.

On a smooth surface, use a ball bearing. That is the ultimate test and will reveal the (inevitable) error in level with far greater precision than a bucket of water.

I once had a play setting up my surface plate "dead level". With a super dry surface and a largish precision ball bearing, you'll never get it perfect, the tiniest movement will have it running off on a curve. Watching some of the metrology vids, you can affect the level on a massive triple A granite surface table just by standing next to it!

 

[skotl]

Happy is good, now what exactly were you trying to level? Please don't say a shelf and you ended up using your iPhone.

Fitting the DRO scales to the mill! Ironically, they just need to be level according to the mill's beds so the level could be out by 73.73639 degrees and it would still have done the job, but I also wanted to ensure the mill itself was level.

 

[Shox Dr]

Fitting the DRO scales to the mill! Ironically, they just need to be level according to the mill's beds so the level could be out by 73.73639 degrees and it would still have done the job, but I also wanted to ensure the mill itself was level.

The scales need to be parallel to the work piece/table other wise the scale will move along a tangent, giving an erroneous reading

 

[DAPPH]

...and you would have established that water is indeed flat.

Err, then what? Transfer a line with a pencil? Fit it with a laser beam?

I strongly suggest if anyone's that interested in metrology, subscribe to oxtools channel on YouTube. A decent machine level would have a fit and probably zoom off the scale if one end was half a pencil line higher than the other. There is a law of diminishing returns for calibrating any piece of equipment and the easiest, most effective way to set it up to within it's own tolerance is to use it to calibrate itself.

Simples ………………. I used a marking knife across the top edges of the water gauge tubes as both were set in the hose to the same height .

 

[Screwdriver]

Fitting the DRO scales to the mill! Ironically, they just need to be level according to the mill's beds so the level could be out by 73.73639 degrees and it would still have done the job, but I also wanted to ensure the mill itself was level.

You'll probably want to set them up with a dial indicator. Setting them up level after setting the machine level merely compounds potential errors. Sweeping an indicator across the body of a scale will give the most accurate result up to the physical precision of the scale chassis. It's nice to have a level machine bed but typically you only do that to make measuring any twist, distortion or wear a bit easier.

 

[Screwdriver]

Simples ………………. I used a marking knife across the top edges of the water gauge tubes as both were set in the hose to the same height .

Cool. Let's talk about compound errors.

Water is a fluid but it's not that fluid, not like say a solvent or light mineral oil. Friction of the glass vial and the springy meniscus at the air boundary will introduce a level error.

You then take an observation, lining up some markings with the water level. Dunno how good your eyesight is (or the precision of the scale) but half a mm is going to be difficult to assess through glass, accounting for the meniscus and with the slight parallax error of position. At that point we rely on the accuracy of the distance from scale marking to the physical top of the tube, be interesting to measure that, it won't be perfect either. I'm liking the "marking knife" incidentally, because of the single bevel, they're about as accurate a physical mark as we can easily do. But again, that has to be perfectly parallel to the top of the tube which itself has to be perfectly flat. Not often I see that on glass tubes which are typically flame softened edges and not ground.

Getting back to the OP, what next? Use those marks to build a perfectly flat surface for the laser level to sit on for calibration? Perhaps use the glass tube to "confirm" the level once it's done, along with all the compound errors it will still be out. It will be out because any purpose built levelling instrument will be using a system of measurement which inherently has greater accuracy than a simple water tube. Otherwise we wouldn't all be buying precision machinist levels or using laser beams. There wouldn't be "spirit" levels either because why not just use water? <see above>

The water system is brilliant for long distance measure where those errors are microscopic in comparison to the distance. Plus of course there's uneven terrain etc. to consider. For greater accuracy, a surveyor could use a laser based system, with the appropriate target, accuracy can be phenomenally precise, within millimetres to the moon etc. But the small size of a portable or handheld levelling unit demands far greater precision to ensure it is accurate over a relatively short distance. Thank goodness they all have such a facility built into the unit itself and thanks to the invariance of a gravitational field, they can easily be used to calibrate themselves with an easy trick of simple geometry.

At least, I thought it was simple...

 

[gaz1]

I wonder what was around when they built the pyramids

WAsnt youtube thats for sure

 

[Screwdriver]

I wonder what was around when they built the pyramids

WAsnt youtube thats for sure

Interestingly it wasn't the old 345 triangle with knots in string either. They used geometry and careful measurements to produce spectacularly accurate pyramids. No one knows exactly how either but string lines simply wouldn't have been good enough to build them as accurately as they did. There's no telling how level they might have been, after all this time those millions of tons wouldn't have just been sitting still.

 

[Munkul]

How many forum members does it take to calibrate a level

Some of you lot would never manage to sort a lightbulb

 

[Screwdriver]

How many forum members does it take to calibrate a level

Some of you lot would never manage to sort a lightbulb

Incandescent or LED?

 

[Climber]

I think you misunderstand what Keith wrote. My reading of it is that at or around 30 feet, the size of vessel he dealt with, it was accurate enough. Why should it not be accurate at smaller distances?

Nope, I understood (and agree with) what he wrote.
I think @Screwdriver has made this point pretty well already, but such a device can't be very accurate for very small distances because of the inherent inaccuracy of the water levels. If you look closely at the water level in a tube, it is dish shaped. That's why we are taught how to read the level of liquid in a test tube. That kind of inaccuracy is insignificant over 30 ft, but much more relevant over 30 cm.

 

[brightspark]

How many forum members does it take to calibrate a level

Some of you lot would never manage to sort a lightbulb

it takes at least 75 posts to solve a simple job god help us if it was anything complicated

 

[eLuSiVeMiTe]

How many forum members does it take to calibrate a level

Some of you lot would never manage to sort a lightbulb

The answer was given in the second post
The answer was given repeatedly throughout the thread.