Every violinist should have a StroboClip HD tuner! (I know that this sounds like a paid-for endorsement, but I can't help it. I am impressed.)
It's small, it fits in any violin case, and (unlike all the other tuners out there) Peterson's "sweetened" violin mode allows you to "accurately" tune your instrument to perfect 5ths, and you can do it in the noisiest environments
At the same time, whether Peterson meant to do it or not, they have also created the greatest tool for teaching and training intonation on un-fretted instruments imaginable, especially the violin. After tuning the instrument, if you leave this tuner clipped on the D string peg while practicing, it will tell you the intonation of every note automatically, as you play it. Fabulous! And because of how the screen reacts to the purity of a note, it also encourages students (and professionals) to put their fingers down properly and play more clearly. The speed combined with the strobo-type display is what makes this all possible, and I cannot say enough good things about it for acquiring quick perfect intonation. It is so much better than any needle, number, or color system could ever be.

In reference to a couple negative reviews I have read:

I agree: DO NOT clip this tuner onto the instrument itself. Especially not one with fine Cremonese varnish.
Unless you have an inexpensive instrument with a hard finish, it will eventually dent the surface and/or mar the finish. Use your judgement!. This tuner is sensitive enough to pick up the vibrations from just about anywhere and anything connected to the instrument. When tuning a violin, clip it on the D string peg while tuning the A and E strings, then clip it on the A peg for the D and G. If you have 4 fine tuners, clip it on the D string peg and away you go.

Sensing the wrong notes depends a lot upon the instrument: its purity of tone and harmonics. At the same time, when using this tuner for improving finger placement, it also helps train the musician to play "pure" notes. This "purity of tone" also relates to the "settling time" issues mentioned, yet I have found no other tuner that is more accurate, easier to use, or faster than this one.

Other clip on options would be nice, especially a wider opening with adjustable pressure. Maybe in the future?

And while the StroboPLUS HD has a better display, etc., and I use it exclusively in the studio; while at a gig, to carry with you anywhere, and for the price, Wow! 5 stars. I will definitely be including this in the school's next video.

Kevin Lee Luthier
Director / The Romantic School of Music
Founded 1715