Sefer Avdiaj1, Yuanchao Yang2, Karl Jousten3, Tom Rubin3. 1. Department of Physics, University of Prishtina, Pristina 10000, Kosovo Serbia. 2. National Institute of Metrology (NIM), Beijing 100029, China. 3. Physikalisch-Technische Bundesanstalt (PTB), Abbestr. 2-12, 10587 Berlin, Germany.