2004/22/EC is the latest European legislation (replacing 73/363/EEC) that lays down the standards of measurement that member states must conform to.
Within the legislation there are ranges of tolerance given to the graduations on measuring equipment such as tape measures. These are defined levels of accuracy that each tape falls within and as such allows you to choose a tape that best suits your needs and budget. Generally speaking the higher the accuracy class, the higher the cost. There are currently three ranges of accuracy, called Class I, Class II and Class III and we look at them below.
Since the legislation covers only metric graduations, strictly speaking the dual metric/imperial marked tapes do not fall within the scope of the legislation. However the manufacturing processes and controls are exactly the same as for metric only tapes, hence the claim on accuracy. Tapes that do not carry a class marking may be inaccurate and could cause problems on tight tolerance work.
This is the most accurate measurement standard, and would normally be found on things like engineers rules where high accuracy is typically needed.
This is the class that C.K™ and Avit™ pocket tapes conform to. A Class II tape will have maximum measurement error as shown in the table on the right.
This shows that at 5 metres the measurement would be correct to within 1.3mm, at 10 metres it would be correct to within plus or minus 2.3mm.
C.K™ Surveyors tapes with glass fibre flexible blades conform to Class III accuracy since the material is much more likely to be affected by stretching or temperature changes.
To get some scale on the difference, where a Class II tape would be accurate to plus or minus 2.3 mm at 10 metres, a Class III tape would be accurate to plus or minus 4.6mm.