In the US anyone can measure a course, but to become a Course Certifier in the US one is appointed by the Chairman of the RRTC. This appointment is based upon several factors as follows: proven to be a good measurer, need for a specific area, recommended by the past Regional Certifier for that area and the Vice Chair suggests an individual. As for AIMS/IAAF, it is a different process, which I will on others to explain.
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