Accuracy of Digital Tape Measures Overview - REEKON Tools

The accuracy of digital tape measures is a complex subject with many factors that contribute to the overall accuracy of the tool. REEKON patented encoding technology is one of the most accurate, repeatable, and reliable ways to measure long distances using a tape measure format

To simplify our message to a broad audience, we state that REEKON products hold a +/- 0.5mm DIGITAL accuracy (unless stated otherwise). 

This accuracy refers to the tool’s ability to interpret the readings on a tape blade within +/- 0.5mm (0.02”) similar to how a skilled user would read a normal tape measure. In effect, replacing your traditional tape measure with a REEKON digital tape should yield readings equal or better than those of a skilled user.

If you are replacing a traditional tape measure with a digital one - the above should be sufficient. However if you are replacing a high-accuracy instrument (think digital calipers, CMM, total station,  etc) with a digital tape measure then you need an in-depth understanding of the tool’s performance and therefore have to look into all sources of error.

1. Accuracy of the Printed Tape Blade and Blade Hook

This is an error that affects all tape measures (digital or analog) as it is related to the manufacturing process of the Tape Blade itself which is a common component for either digital or analog tapes.

Tape measures are put into 3 different classes of accuracy:

• Class I (+/- mm) = 0.1 + 0.1 * L
• Class II (+/- mm) = 0.3 + 0.2 * L
• Class III (+/- mm) = 0.6 + 0.4 * L

Where L is in meters (m) and the final accuracy is measured in millimeters (mm)

In the equations above the fixed (constant) term is a result of the Tape Blade’s Hook installation accuracy and the scalar term (the term multiplied by distance) is a result of errors inherent to the printing process.

REEKON Digital Tape measures use either Class I or II tapes where the Hook is inspected to being installed within +/- 0.25mm.  An individual inspection would be needed to confirm compliance but, from our internal inspections and testing, most REEKON tapes meet Class I standards.  

2. Change in Temperature from 25°C Baseline

This is an error that affects all tape measures (digital or analog) as the tape blade is made out of steel which expands / contracts with temperature. Any measurement done at a temperature higher or lower than the temperature the tape was printed at will be subject to this error.

Expansion error (+/- mm) = (0.0117 * L * ΔT°C)

• Where L is in meters (m) and the final accuracy is measured in millimeters (mm)
• Where ΔT°C is change in temp from 25°C baseline

3. Digital Encoding Repeatability

For a traditional (i.e. analog) tape measure the user has to make a judgment as to what is the reading on the tape. For a digital tape measure this is done digitally. This process introduces some random error which we refer to as the repeatability of the encoder

REEKON’s encoding technology is repeatable within +/- 0.02mm (2 sigma confidence interval) which is such a small number that can be ignored from the accuracy budget

4. Rounding Error

For practicality purposes REEKON Tools Digital tapes round their readings to the nearest 0.5mm (or 1/32”) (unless stated otherwise). This is not a limitation of the technology but a product level decision to simplify readings.

In the worst case, the rounding error will add +/- 0.25mm to your measurement.

Total Measuring Accuracy 

Combining all the above, the total system accuracy is as follows:

Accuracy (+/- mm) = 0.50 + (0.2 * L) + (0.0117 * L * ΔT°C)

• Accuracy is stated in 2 sigma confidence interval
• Where L is in meters
• Where ΔT°C is change in temp from 25°C baseline

For example, a measurement made at 5 meters at 30°C will have a worst case error of +/- 1.8mm

We encourage customers concerned with accuracy to reach out to us and we would be happy to walk through the above and any other questions in more detail.  REEKON Tapes are made and inspected more than any other production tape on the market and while accuracies are generally much better than the worse case scenario, we share the above to be as transparent as possible.