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Posted
1 hour ago, Pocster said:

A load of guys trying to do accurate measurements. None of you know what 6 inches is !

🤫 glazing is much easier to measure correctly

Posted

>>> I have a high tech equivalent, a long tube connected to a pressure meter, and giving height difference digitally.

 

That’s interesting - tube has water in it? Digital pressure meters are expensive, no?

Posted
3 hours ago, Alan Ambrose said:

tube has water in it?

I think it is oil. The height difference creates a pressure which is converted into mm.

It isn't perfect as i reacts to temperature change and so needs resetting.

A water level is absolutely fine, just more fiddly as a one person operation.

Posted
8 hours ago, SteamyTea said:

Not with a theodolite.

I have one but hasn't been used in 30 years.  Pythagoras works more quickly so I DO use 2 x 60m tapes.

 

In case interested. When being trained, they sent us round a housing estate with an optical level, so about 1km and several blind corners.

Training was by ex mining surveyors on the basis that they could do it underground and unsighted, so were very good.

We had to arrive back at the same hilti nail point with 3mm maximum difference. There was no point in cheating as it was training.

Key to success was equal back and fore sights, so any errors cancelled out, and a very distinct surface (change point) to place the staff on.. We would take 6 readings, score out any rogues  and use the mean.

All done by hand: pencil in a potentially soggy book.

The chainman rocked the staff on the point, which made the numbers appear to go up an down, and the lowest of them was the most accurate.

In reality, the chain men (young lads  really) couldn't choose the good change points so for training it was all Engineers.

 

In real life I once had completely nonsensical numbers. I asked the chainman if there was something wrong with the official point (a metal spike) and he admitted he couldn't find it in the bracken so had used his initiative and put the staff on his toecap. 

 

Theodolites for angles.... way more tricky, especially through woodland or over cliffs  .. another day.  And then there are tacheometers for slope distance and height change.

 

It all sounds very technical but our other main tool was a 14 lb hammer for banging in posts.

Posted

Re: Ziplevel

 

Says it has gas and liquid and a reference cell. Reads in cm and I wonder if that gives a clue to accuracy. Claims 0.25mm / 0.2% reading, which I guess means 2mm per metre height difference. I wonder if that's +-2mm? See below.

 

There's a competitor called the Nivcomp, claims +-2mm.

 

ZIPLEVEL® is a high precision pressurized hydrostatic altimeter. It works much like an aircraft altimeter that measures the weight of the air above it except that ZIPLEVEL does not use the atmosphere to measure elevation. Instead, ZIPLEVEL is a pressurized system that measures the weight of a proprietary liquid sealed within its Cord relative to a Reference Cell in the hub of its reel. This makes ZIPLEVEL 10,000 times as precise as an aircraft altimeter and immune from both barometric pressure and altitude changes. It's internal pressure prevents bubbles from desorbing from its liquid when under vacuum when the Module is above the Base Unit and is one of our powerful patented features.

Posted
58 minutes ago, Alan Ambrose said:

in real use?

Used rigorously i'm happy it is +/-  2mm, maybe much better than that.

That's a hunch, and I haven't checked it against known levels.

 

Where I've had issues was in doing levels over a period of time in hot weather.  The tube/gas would be heating up I suppose.

I learnt to reset and start again.

But doing, say, 20 points around a perimeter wall or over a slab Im very happy with it. Especially that distance is inconsequential.

 

The biggest downside is that it is not compatible with a busy site, as the tube is either in the way or vulnerable. 

I wouldn't want it in a trench doing drainage for example, with an excavator and shovels and pipes being moved.. But would be happy in the empty trench, setting or checking levels.

 

The biggest upside is the reverse of that. I can quietly do surveys or check other people's work, on my own and at my own pace, with thinking time.

An advantage I haven't mentioned is with large height differences.  This could be used with the base downstairs and the gauge up a floor or two. eg no excuse for joists being set wrongly.

 

I used this mostly on big projects to set out levels for steel base plates.  After 4pm.  I could stack shims and recheck them, or write a number on the concrete.

Also to check slab perimeters before block or sole plates went in.

And if there was any serious doubt about what someone had built, to check it on my own after hours,  without creating friction.

Very happy with it.

 

Does that help for your own circumstances?

 

Posted

Well I need to get these levels down fairly promptly so I'll have to find a way to get more accurate readings with the laser I have. But for the future, who knows.

Posted
51 minutes ago, Alan Ambrose said:

Well I need to get these levels down fairly promptly so I'll have to find a way to get more accurate readings with the laser I have. But for the future, who knows.

But some clear braided hose pipe 19 mm diameter. Set two stakes at each end of your slab and purge with the garden hose. Get some drain dye and fill a canister. Tape a funnel to one end of the hose and pour in the dyed water until it comes out the other end. Don't use too much dye just enough to let you see some colour. 

 

Now you have a water level. To give you confidence mark the bottom of the miniscus on the stake. Then with a helper (easier) swap the ends of the tube and if you don't get exactly the same reading then you have air in the pipe.

 

You can move one end of the pipe anywhere you want as it will maintain the datum level. To do this you can make out of timber a tripod so the water doesn't spill out the tube. 

 

Once finished stopper up the pipe so next time you want to use it the set up time is less. And once finished the build it reverts to a garden hose. 

Posted
5 hours ago, Alan Ambrose said:

more accurate readings with the laser I have.

So use the equal sight distance principle.

eg, if you set the instrument in the middle of the room it minimises errors. 

 

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