Measurement results have to be internationally comparable. This demand is assured by the relation of the measurements results to standard references, normally maintained by a national standard body. Accuracy of those standards is assured by an unbroken chain of international comparison measurements. Our calibration standards and calibration standard measurement equipment is traceable to international accepted standards of NIST, USA (National Institute of Standards and Technology).

”Traceability“ describes the procedure of comparing the display of a measuring device with the original reference source for the measurement in one or more steps. Each step has to be calibrated against a standard whose metrological quality was also certified against a standard of higher order, creating a calibration hierarchy from the national working standards through a laboratory.

Traceability is characterised by some basic essentials:

• An unbroken chain of comparisons which can be traced back to stated national or international references, approved by the parties involved.
• Measurement uncertainty has to be calculated for each intermediate reference standard using approved methods. It has to be stated in a way that allows calculating the over-all uncertainty for the measuring chain.
• All calibration steps have to be accomplished following generally accepted and described methods, results have to be documented.
• Laboratories or others who accomplish one or more steps in the measuring chain have to prove their technical competence.
• Calibrations should be repeated after reasonable periods of times. The length of this period depends on variables such as the required certainty, the frequency of use, the way of using it or the constancy of the device.

Does the setting of the slit match with the specifications on the certificate? Other slit settings can cause errors in the peak maxima.

The absorbance values of the neutral density glass filters do depend on their thickness, and so they can be available on customer request.

The holmium oxide glass is slightly hygroscopic, so the covering is a kind of water film. Measurements are not affected. The filter may be wiped with alcohol and a soft tissue to remove the film. As a basic principle the filters should be stored in a dry place.

To check the correctness of the values given on the certificate, the calibration standards should be recalibrated at regular intervals. The periodicity of these intervals should be determined by the user and depends on the laboratory environment and the conditions of use, just like the total lifetime of the filters. To define a statistical basis for establishing the recertification interval it is recommended to have all calibration standards recalibrated every 12 months in the first two years of use. Afterwards an interval of recalibration should be chosen which seems to be suitable based on the values obtained this way.