code: func (f *Factory) Gauge(options metrics.Options) metrics.Gauge {
  	gauge := &gauge{
  		gauges: make([]metrics.Gauge, len(f.factories)),
  	}
  	for i, factory := range f.factories {
  		gauge.gauges[i] = factory.Gauge(options)
  	}
  	return gauge
  }
docs: // Gauge implements metrics.Factory interface