code: func (p *PrometheusReporter) ReportGauge(metric string, labels map[string]string, value float64) error {
  	g := p.gaugeReportersMap[metric]
  	if g != nil {
  		labels = p.ensureLabels(labels)
  		g.With(labels).Set(value)
  		return nil
  	}
  	return constants.ErrMetricNotKnown
  }
docs: // ReportGauge reports a gauge metric