Danny,

It is not really hidden or secret and mentioned in the help under "What's new".

In short: The setting can be found under File | Options. It is labeled "Unit of Measurement".

I don't know why the automatic function returns Imperial instead of Metrics for your region as the function used uses the current user locale. If you can show the exact locale choices you made (the screenshot only shows the values) we can see if we can duplicate this.