NewCounter returns a new Counter backed by a Prometheus metric.

NewGauge returns a new Gauge backed by a Prometheus metric.

NewHistogram returns a new Histogram backed by a Prometheus Histogram.

NewSummary returns a new Histogram backed by a Prometheus summary.

RegisterCallbackGauge registers a Gauge with Prometheus whose value is determined at collect time by the passed callback function.

Prometheus has strong opinions about the dimensionality of fields.