Teaching Assistent physics, Univ Botswana (1982)
Grade I qualified teacher in physics (1985-)
Technical responsible scientist for temperature and humidity standards of NMi/VSL (1986-2004)
Teacher at and writer of courses of NMi/VSL (1989 -2005)
Representing NMi/VSL at the CCT (1996-2003) and rapporteur for CCT-meetings of 2000 and 2001. Chairman  CCT Werkgroep 8 (2002-2004)
Chairman EUROMET TC-Therm (2001-2004)
Owner MartinDeGroot Consultancy (2004-2005 & 2008-)
Project- and quality manager Contell-IKS (2005-2007)
Teacher for Kelvin-Trainingen (2004-)

ISO/IEC 17025 Technical assessor for RvA (1987-),UKAS (1995-),SANAS (2003), PCA (2005), ISRAC (2004-2006), INAB (2010-2011) and BELAC (2004-)
ISO/IEC 17025 lead assessor for RvA (2008-) and INAB (2010-2011)
Many of the afore-mentioned Conformity Assessment Bodies (CAB's) are members of European Accreditation and all are signatories to the ILAC  MRA

Author of some 100 publications on thermometry, humidity and uncertainty