If you have a metric that you want to display across multiple dashboards, you don't need to make a copy of each one—Each copy would count against your metric limit and if you needed to make changes in the future, you would have to edit each one.
Instead, you can "share" the metrics between dashboards. This way it will only count as one metric and any changes made to one on any dashboard will update that same metric on other dashboards.
Sharing a Metric
To share a metric, click on the metric action menu at the top right and select "Share Metric". A window will pop up with a list of dashboards you can share the metric to. Click on each dashboard where you want to include this metric, then click "Submit". The metric will start at the top left of each dashboard, then you can move and resize each instance of that metric on each dashboard.
Moving and resizing the metric will not affect any of the others, but making any changes in the metric builder will affect all instances of that shared metric.
Deleting a Shared Metric
If you delete a metric that is shared among multiple dashboards, it will not affect or delete the other instances of the shared metric. It will still prompt you to confirm the deletion. If you want to see if that specific metric is shared on other dashboards, click on the "Metric Info" button next to the metric name. This will give a list of other dashboards (if any) the metric is shared with.