Single value error when creating a measure

Hi, 

I am new to PowerBI and  am creating a measure for calculating uptime %. I tried to create the measure, but got an error because one column wasn't aggregated. The error stated, "A single value for column Total Units in table Location_Table cannot be determined."

How can I calculate the uptime % for every Location? Location is the unique column in the Location_Table. Here's the tables:

For Faulted Units, I am counting the keys: COUNT(Fault_Table[UnitKey]).

Here's the formulas:
Working Units = Total Units – Faulted Units
Uptime % = Working Units/Total Units

Please let me know if I can provide more information.