code: func (m *metricUnit) SpaceScale() SpaceUnit {
  	d := m.SpaceDim()
  	if d == 0 {
  		panic("no space scale on unit")
  	}
  
  	return SpaceUnit(1<<28 | (uint32((m.repr>>16)&0xF))<<16)
  }
docs: // https://docs.rs/hornet/0.1.0/src/hornet/client/metric/mod.rs.html#398