How to calculate the total locked XTZ?

Using the TZscan.io Stats – Key Numbers dashboard, how can I calculate the total locked XTZ in the system? And shouldn’t this be a KPI measure by itself? Since delegators can very easily move their XTZ I don’t consider that locked, especially since all the exchanges will be auto delegating for their account holders.

Total frozen balances
Total frozen deposits
Total frozen rewards
Total frozen fees
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Total Frozen XTZ ?

Also, what is the difference between ‘Total frozen deposits’ and ‘Total frozen balances’?