Conventional reference level for a global unified height system L. Sánchez; Deutsches Geodätisches Forschungsinstitut (DGFI), Germany N. Dayoub; Tishreen University, Syria R. Čunderlík, K. Mikula, Z. Minarechová; Slovak University of Technology, Slovakia Z. Šíma; Astronomical Institute, Czech Republic V. Vatrt, M. Vojtíšková; Geographic Service of the Czech Armed Forces, Czech Republic On behalf of the WG on Vertical Datum Standardisation