This may be a pretty daft question to most of you out there, but I do need to clear it up.
Normally, I use an electric guitar tuner on the E string, and tune the others strings in order, at the 7th fret, against the E string. I noticed that when the mandolin is in tune against the other strings, and sounds correct to my ears, the D string is not correctly tuned against the tuner.
Today I tuned all the strings against the tuner. I found that the mandolin is not only easily tuned but sounds brighter and more pleasant than normal. The curious thing is, and here is the question, the strings are not tuned correctly against each other when fretted at the 7th. They are less than half a tone out.
Can someone explain why that is?