If you have had an export surplus for the last 5 years, your currency is undervalued.
How to tell if your currency is overvalued?
If you have had an import surplus for the last 5 years, your currency is overvalued.
Why do I mention this?
Brazil is whining its currency is overvalued, despite having an export surplus of $28bn (From Wolfram Alpha).
I've forgotten how to get Wolfram