Here's a link to one of my blog posts that might be helpful in figuring out how to tune your dulcimer:
In the blog post there's a link to a real online keyboard where you can HEAR the notes D3 and D4 for example. You'll want to e sure to tune to the notes in the correct octave so you don't break your string.
Those irritated by grain of sand best avoid beach.
-Strumelia proverb c.1990