Found this on Hardanger tuning - presumably those of us without the instrument itself can just use the overstring tuning:

"Hardanger fiddle overstrings are tuned many different ways but the most common tuning is standard violin tuning except for the G which is raised to an A. The understrings are tuned to different tunings depending on how the overstrings are tuned. With the overstrings tuned to ADAE the understrings will usually be tuned to DEFA. If your hardanger overstrings are tuned to standard violin tuning, GDAE, then your understrings should be tuned to DEGA. "

Cheers
Sarah