For anyone wanting to format the number on a tooltip …
Machine: [bold]{name}[/]
CPM: [bold]{valueY.formatNumber("0.0")}[/]
Date: [bold]{dateX.formatDate('yyyy-MMM-dd')}[/]
Time: [bold]{dateX.formatDate('HH:mm EEE')}[/]
More on the AM Charts website at Formatters – amCharts 4 Documentation.