Hope you don't mind me adding to this? My main instrument is cello and I play in a number of amateur orchestras. In the hubub at the start of a rehearsal, it's difficult to hear the cello over assorted brass and woodwind, so I tune with a Korg chromatic tuner (which I've found to be reliable - I've had it 10 years now). At the start of the reharsal proper, the oboe provides an A which we all check our tuning against. It's usually more-or-less bang-on (because the oboist generally has a tuner switched on to check that hey are giving a steady A = 440 note.
I can tune without it and I can tell if I'm out of tune quite easily too, but he tuner cuts out some faffing around and gets me round the noise. String instruments don't like temperature changes as it effects the length of the strings and they take a while to reach equilibrium.