How to determine whether two separate tiled floors at ground level are even with each other?

My kitchen floor is tiled three-quarters of the way across. The last quarter was finished with carpet as the so-called "dining area". Adjacent to the kitchen is a utility room with washing machine, downstairs lavatory etc. Its floor is also tiled.
I would really like to replace the carpeted area with tiles that match the other floors, but I can't be sure there isn't a slight incline from one of the floors to the other.
One way I can think of measuring how even the floors are would be with two wood blocks, a very long straightedge and a spirit level. But I don't have anything that long (at least 2.5m) that is dead straight.
Another idea is to somehow make use of the laser distance meter I have. Supposing I placed the meter on one tiled floor and a marked piece of card on the other. I could see where the laser beam hit the card, then swap the two over and repeat.
Any ideas? Maybe a taut length of string could be used somehow?
I first thought of just pointing the laser meter and the ceiling from floor level, but the ceilings in kitchen and utility room are not exactly at the same height because the utility room is an extension to the garage which is a separate structure to the main house. (Separate, but "lean-to".)
MM
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MM wrote:

You'd probably not notice it even if there was.

Get some clear piping and not quite fill with water (add food-colouring if necessary to make it easier to see)
place two equal height items (bricks? chairs?) on the two floors and line up the pipe to see if the level is the same ...
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On 03/09/2017 16:11, Andy Burns wrote:

Laser level is your friend here. I know the pipe is the age-old traditional method but effects of surface tension and greasy stuff in the pipe bore makes this slightly less effective than you might expect.
Not a tool I use very often, but brilliant in the right application.
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newshound wrote:

OK when you've got one, but ss's job hardly sounds enough reason to buy one ...
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Rent one.
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Andy Burns wrote:

oh, sorry MM's job ...
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On 03/09/2017 16:35, newshound wrote:

Add detergent to the water?
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On 03/09/17 16:11, Andy Burns wrote:

Yes I remember using what we called a water line to mark 2 or more equal heights on a wall at about 4 meters above ground level in a large open building.
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"MM" wrote in message

Rotating laser level on tripod with staff
http://www.laser-level.co.uk/products/spectra-laser-levels-and-laser-accessories.html
My (pretty old now) one will tell levels within 1 mm over short (sub 50 metre) distances on the fine range
Andrew
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On 03/09/17 16:04, MM wrote:

If it's that hard to measure, you won't see it in the finished result.
I have 1cm drop over about 1m from kitchen to lobby, all done in the same tiles and it's invisible.
The main thing is that you don't have localised discrepancies and a 6' level will be good enough to gauge that.
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Assuming you use 4pint milk containers, have a suitable sacrificial length of garden hose and a suitable size drill bit.
Drill holes in the sides of the milk containers such that the hose is a tight fit. A bit of leakage won't affect the result in any case.
Fit the hose and place the containers on the two surfaces.
Start filling one of the containers with water until the container at the other end is three quarters full.
Very carefully mark the level on each of the containers with a permanent marker.
Empty the containers into a bucket and then measure the difference in the height of the marks on the two containers.
michael adams
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Just remembered - the mark is first made on the first container which is filled it up to that mark - this then reduces the impact of any leakage assuming a perfect fit can't be achieved; as the second mark can be made straightway. The holes in the containers are in the sides 1/4 the way up and the hose rests on the floor.
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On Sun, 3 Sep 2017 21:15:03 +0100, "michael adams"

This sounds like the cheapest solution, although I like the idea of the laser levels! They do seem handy for a lot of jobs, especially picture hanging.
I only buy 1 pint milk containers, but I'd be prepared to buy 2 4-pint ones over two weeks! I don't usually buy larger than 1 pint, because I reckon the milk stays fresher for longer in unopened containers.)
Thanks to all for your suggestions.
MM
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On Sun, 3 Sep 2017 21:15:03 +0100, "michael adams"

This sounds like the cheapest solution, although I like the idea of the laser levels! They do seem handy for a lot of jobs, especially picture hanging.
I only buy 1 pint milk containers, but I'd be prepared to buy 2 4-pint ones over two weeks! I don't usually buy larger than 1 pint, because I reckon the milk stays fresher for longer in unopened containers.)
Thanks to all for your suggestions.
MM
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4pt milk containers have a "waxy" finish. This may be a component in the plastic to enable easy mould release. This can make them difficult to write on or mark with any degree of precision unless an area is first cleaned with white spirit. Ideally vertical address labels can be stuck on the containers which can be marked with something like an Edding Fineliner. Or to save this faffing around just leave the original labels on the containers and mark on the edge of the labels. As the labels only go half way up this means the levels will need to be lower than half way. Water is handy compared with a laser when there's no direct line of sight although this can be got around with a mirror. As the beam has minimal width the angle isn't crucial. Theres no actual need to cut the hose which could lie coiled on the floor ; it would simply make filling the whole thing more time consuming.
michael adams
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