Note: if you want to set different units in the same table, you need to use the advance editor mode! 

If you are on the simple editor mode

Click on the button under "Table unit conversion". You will see a dropdown from which you can select the unit to convert from and to!  So lets say your table measurements are all in inches, you would want to select "inches -> centimers" options

To change the unit system, click on the purple button.

After the unit is set up, you will now see unit conversion button show up!

If you are on the Advanced editor mode:

The Table unit conversion button is still there. So you can follow the same steps above to set units.

What is different in the advanced mode are the black arrows above each column (if unit direction is column) or each row if unit direction is row. 

Click on the black arrow allows you to set the unit on a per measurement basis in cases when you want to have multiple units in the table.