Some tuners can tune to a dozen or more different scales, only two of which are the common Just tuning or Equal Temperament tuning. With one of these, the tuner might be set to a wrong scale, which would make intervals (as when bowing G and D strings together) sound "out of tune." I once thought I wanted one of those tuners, but abandoned the idea when I found out one of that kind cost more than both of my mandolins, so I doubt if that's the problem here.

The "wound" violin strings typically have a "soft core" with metal wire wound around them. If the string was "coiled" in the package it may need significant stretching just to straighten it out so that it will hold the pitch you tune it to. Tuning up one note, playing (bowing) the string some, and then tuning back down may give a better "hold" on the note you tune to. This effect is more noticeable if the string was coiled up "on the shelf" (or in the fiddle case) for a long time before being installed. While the traditional "gut" core was fairly elastic, some core materials used now (plastic) are "creepy" and will continue to stretch for quite a while even after you get them "apparently straight."

The fiddle bridge is a "pivot" for the strings, and it's intended to equalize the tension between bridge and nut with the tension between bridge and frog. Sometimes, if two or three strings have already been installed and tuned, the last one or two strings can't "swing" the bridge to even things out. With the "playing end" tuned, bowing may shake the string enough for it to "slip" on the bridge, which generally lowers the string from the pitch you tuned to. A commonly suggested procedure is to loosen all the strings to about the minimum tension that makes a tone when you pluck them (enough to hold the bridge in place), then bring them all up to pitch together, in small steps. An alternative "quicky method" is to lift the offending string up off the bridge by grabbing it right at the bridge, lifting enough to assure that it can "slip," and letting it back down.

While bowing technique theoretically doesn't affect the "pitch" it can significantly affect the perceived pitch by altering the overtones contained in the sound. Unlike a guitar where you stretch the string and let go, the fiddle bow stays in pretty much constant contact, so the string motion is a "stick-slip" mess very similar to a piece of chalk screeching on a blackboard (for those old enough to remember blackboards/chalkboards). On a guitar, you can get an almost pure tonic by plucking at the midpoint of the string, but richer sound about 1/5 of the way up from the bridge. Where you pluck affects the "quality" of the sound. The fiddle does the same, but additionally gets "content" from the chalk-screech excitation, so that bow pressure and speed also affect the tone. A "note" perfectly at pitch can sound like it's somewhere else with sufficient screech harmonic content.

An extremely remote possibility is that when strings are changed on a fiddle, if they're all removed at the same time, the sound post may have "dropped." This makes the top plate "too flexible" to do much of anything right. The description of symptoms in this case doesn't sound "quite right" for a missing post, so it's mentioned only for the sake of completeness. The post should be visible through the sound holes to be sure whether it's still up - or just shake the fiddle and see if it's got a new rattle inside.

John