                  22,
                  23,
                  24,
                  25
                ],
                type: 'numeric',
                tickPlacement: 'on',
                tickAmount: 'dataPoints',
                labels: {
                  showDuplicates: false,
                  formatter: function(value) {
                    // Value is undefined if all series are collapsed
                    return value !== undefined ? value.toFixed(0) : ''
                  }
                }
 