Historical calibration certificate issued by Kipp & Zonen for CMP21 pyranometer serial number 120894. The certificate number is 012109120894. According to records maintained by the depositor, the instrument was subsequently operated at Chilbolton Observatory as part of the Chilbolton Facility for Atmospheric and Radio Research (CFARR). At the time, CFARR was operated by the Science and Technology Facilities Council (STFC), managed by the National Centre for Atmospheric Science (NCAS), and funded by the Natural Environment Research Council (NERC). The certificate was issued on 01 May 2015 and deposited retrospectively in 2026 to support the provenance of observations archived by the Centre for Environmental Data Analysis (CEDA). This record forms part of a chronological series of calibration certificates for Kipp & Zonen CMP21 pyranometer serial number 120894; links to the adjacent calibration records are provided under Related works.