Violins can be tuned up by different means.  The ways I know of are tuning strictly by ear, tuning by comparing each string against reference notes like the tuner on the Fiddlerman.com site), tuning from an electronic tuner, tuning by playing 5ths (after tuning one string by a reference note or electronic tuner), and tuning by harmonics (again, after tuning one string from a reference or electronic tuner).

I use a combination.  I tune the A string from the electronic tuner, then I tune the other strings to it by the harmonics, and than I do  final check by playing a stroke on each of the 5ths (G+D, D+A, A+E) just to make sure.  My reasons are:

1.) I have a good ear, but not perfect, so I don't tune strictly by ear.

2.) I tune other stringed instruments by harmonics, so I'm used to it.

3.) Checking the 5ths, if the 5ths are right then you know for sure the instrument is in proper tune.  But I find it harder to hear which note is actually out when playing a 5th than when playing them in unison with harmonics.  Kind of pointless, since if the harmonics are in tune, then the 5ths always are, but it's just sort of the last check "finishing touch" sort of thing to me.

4.) Every electronic tuner I've ever used is usually a tiny bit "out" on some notes.  Theoretically they should be perfect, but they always have to be designed, programmed, made and calibrated by people who get an hourly rate and who usually just aren't musicians.  "Spec" for quality control in any factory is always based on how good it has to be for a fair number of units to sell every month, and allows some leeway because it would just take too long to make every unit "perfect".  So somebody in engineering or quality control decides what is "close enough".  It is just one of those unavoidable compromises that allow electronic tuners to be cheap enough for most folks to afford.  They're ok for rough and ready quick tuning, and nice when trying to tune when it is noisy, but I usually like to check the harmonics and 5ths and adjust for fine tuning.

I also tune from the bowed notes, since it seems to me that they are just a tiny smidgeon sharper than plucked notes. 

Anyway, it takes a lot longer to type about it or probably even read about it than it takes to actually do it unless the instrument gets badly out of tune.  That happens sometimes because pegs get bumped or sometimes get messed with by my autistic son who likes to see the pegs all turned neatly in exactly the same direction, or the bridge needed a little adjusting or etc.

I was just wondering how other people maybe tune differently, and why.  Always looking for better ways, if anyone knows some.