Oops - I guess that needs to be better signposted... If you go to the currency page in the dialog (where you're creating USD), there's a "Default Currency" dro

Oops - I guess that needs to be better signposted... If you go to the currency page in the dialog (where you're creating USD), there's a "Default Currency" dropdown in the main section on the right. You might need to close out of any currency you're editing, but hopefully it's reasonably prominent once you do.