NewCounter creates an expvar Float with the given name, and returns an object that implements the Counter interface.

NewGauge creates an expvar Float with the given name, and returns an object that implements the Gauge interface.

NewHistogram returns a Histogram object with the given name and number of buckets in the underlying histogram object.

Counter implements the counter metric with an expvar float.

Gauge implements the gauge metric with an expvar float.

Histogram implements the histogram metric with a combination of the generic Histogram object and several expvar Floats, one for each of the 50th, 90th, 95th, and 99th quantiles of observed values, with the quantile attached to the name as a suffix.