It has 2 rate counters: one ticks twice a seconds, another one can be manually updated with 'update-rate-ctr' command via vty.
The raw value is sent via statsd protocol. If you install "netdata" monitoring tool than you can open http://localhost:19999 in browser and observe live counters monitoring under "StatsD dummy" without any additional setup.
Opening osmo-stat-dummy.html in browser while both netdata and osmo-stat-dummy are running will show dimensioned (per min/hour/day) rate counters as well as raw data.
The latter is handy for troubleshooting and comparing libosmocore's internal rate counter computation.