The Cobalt System Metrics Daemon starts early after boot on a Fuchsia system and periodically measures several system metrics and logs the values to Cobalt. The daemon is not part of the Cobalt telemetry system but rather a client of it that happens to be owned by the Cobalt team.
If you would like to start measuring a new system metric on Fuchsia you might consider adding the instrumentation to this daemon. That would be appropriate if