It seems that the Haddock documentation for Data.Metrics.Meter does not specify the units for oneMinuteRate, fiveMinuteRate, fifteenMinuteRate and meanRate.
The meanRate is given as number of events per picosecond, whereas the exponentially weighted moving averages are given as number of events per five second timeframe.
Probably it makes this package easier to use when this is clearly stated.