Before:

After:

1. In the data pane, right click on the field (in this example, Weight) and click duplicate
2. Put the newly copied field onto the Text shelf
3. Go to Worksheet at the top left of Tableau and click on Tooltip
4. Place the copied field onto the tooltip as desired
5. Right click on the view and click on Format
6. Format the fields' decimal places as desired e.g. in the Axis tab for the original field and the Pane tab for the copied field

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