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November 27, 2025
In this article, James Dare, European Director of CoGri Group, looks into a critical aspect of floor measurement and surveying (understanding the difference between point accuracy and property accuracy.)
James highlights why relying solely on point measurements can be misleading when assessing high-tolerance floors.
When floors are measured, everything starts with a simple point height.
Whether you use a scanner, a laser level or a traditional instrument, each point you record carries a certain amount of uncertainty.
Where things start to slip is when those points are used to calculate properties such as flatness and levelness. This is where a lot of people assume that the accuracy of the property is the same as the accuracy of the individual points, but it never is.
I have spoken about instrument accuracy in two previous LinkedIn posts where I looked at the suitability of laser scanning for tight tolerance work and carried out a study on the actual precision you can expect.
You can find these posts and related articles here:
UK Concrete Society – Laser Scanning for High Tolerance Floors – Is it Really Suitable?
The same message keeps coming up.
Point accuracy is not the same thing as property accuracy.
Once you combine several uncertain values, the final result will always be less precise than any one of the values that produced it.
There is a simple reason for this:
Whenever you compare or combine several measurements, the small errors in each one carry through into the final result. The more values you combine, the more the uncertainty grows.
As an example:
If a single point has an uncertainty of about ±0.8mm, then a two-point property that compares two of those values is already closer to ±1.1mm in uncertainty.
A three-point property grows again and is often around ±1.4mm.
(More detailed calculations about how the property uncertainty is calculated are included at the end of this article here.)
This is not a minor detail.
It means that even if your scanner or instrument can consistently record points to less than a millimetre, the properties you calculate may not be accurate enough to judge a tolerance that sits around the one-millimetre mark.
See figure 1 below.
Modern automated warehouses and high tolerance systems are often working within very small property limits. When property limits are around one millimetre, using a method that can only provide a property level accuracy of ±1.1mm or ±1.4mm creates obvious problems.
First, you can end up with false negative results where the measurement error hides a genuine local defect.
Second, you can get false error results where perfectly acceptable areas look out of tolerance simply because the method is not precise enough.
Both outcomes cost money, time and create unnecessary risk for all parties.
If point-based methods or 3D scanning are going to be used for tight tolerance work, a few things should always be made clear.
Without this, we end up with impressive looking surveys that cannot fully support the decisions they are being used for.
Point accuracy on its own does not tell you enough.
Once you start using those points to build properties, the uncertainty grows. This is a basic part of measurement theory, but it is something that is still overlooked far too often in our industry.
Scanning is a fantastic tool, and it is improving all the time, but like any measurement method it needs to be understood properly. If we want reliable results for high specification automated facilities, we must be realistic about how much confidence each method can genuinely provide.
At CoGri Group and Face Consultants, we keep challenging the capabilities of 3D scanning. We run ongoing studies with a range of scanners and survey methods to reduce uncertainty as far as possible and check every result against proven high tolerance equipment.
If you want absolute confidence in your floor data, talk to us today.
The point uncertainty is taken as 0.8mm.
Property uncertainty is calculated using standard error propagation, where independent uncertainties combine through the root sum of squares method.
0.8² = 0.64
0.64 + 0.64 = 1.28
√1.28 = 1.13mm
Rounded to about 1.1mm
0.8² = 0.64
0.64 × 3 = 1.92
√1.92 = 1.38mm
Rounded to about 1.4mm
For any questions or if you would like to organise a meeting or workshop to discuss best practices for testing high tolerance floors, please reach out.
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