WARREN MAY DULCIMER

Is anyone familiar with Warren May dulcimers? This is about 20 yrs old or so, wooden peg tuners and no 6 1/2 fret. after measuring to the 7th fret and doubling the distance, I set the bridge at 26 1/2", tuned it to DAD and checked the notes up the fret board. I found the first 3 notes are flat, 4th is ok , 5th and 6th sharp and 7th ok. If I tune just a little sharp the most are close except at 2nd fret, its still flat.

I compared several fret charts to actual measurements from nut and found some frets as much as 1/4" difference from the charts for fret calculations. I am fairly new to dulcimers and am looking for suggestions. I want to put a 6 1/2 fret in but am thinking I should locate it with a tuner as opposed to measurements. Any comments or suggestions?

Bill R