I still hate those who will switch to the confusing mess of crap known as the US Imperial system but...
Documents>Arma 3 Alpha - Other Profiles>User name>
Then open Username.Arma3alphaProfile in Notepad (++) and around line 120 there should be 'useImperialSystem=0;' change that to 'useImperialSystem=1;' and you should be rocking the retarded roller-coaster again.
Got this of Google
And I just checked it and it's confirmed, on your PC it's prob set to 1 change it to 0.
Word to the wise, War is a necessary undergoing of change, the evidence is all around us, War formed and changed The United States, War formed and United the United Kingdom, War formed the countries now part of the European Union, i'm just saying!