Machine Diagnostics provides a real-time view of all data items that are being streamed from a machine and updated every second. The format of this data is in MTConnect, which MachineMetrics uses as it's internal data structure. Much of this information is available in various reports, and can be viewed historically in the Event Log. Some of the data isn't used in reporting, but is stored for possible future analysis and reports.
To access diagnostics, click on a machine tile in the dashboard, and select the tool icon. Or if you are already in machine reports, just select "Diagnostics" from the left hand navigation.