Man pages matching name pmregisterderivedmetric in section 3:

pmRegisterDerivedMetric.3.en	debian 10 / libpcp3-dev
pmRegisterDerivedMetric.3.en	debian 11 / libpcp3-dev
pmRegisterDerivedMetric.3.en	debian 12 / libpcp3-dev
pmRegisterDerivedMetric.3.en	debian 13 / libpcp3-dev