M. Allaart (KNMI) – Brewer #189 beginning in 2007. Brewer #100 from 1994 to 2006. Data in the NDACC database begin in 1994. Intercompared with traveling standard in August 2012 and in September 2014. Additional calibration for Brewer #189 in 2009-06, 2017-05, 2020-05.