Some of the greatest modern gadgets helping out bluegrass pickers nowadays are electronic tuners. Some of you may not remember the times before there were such things, but I can guarantee from experience that the tuners are a huge help in getting and keeping a jam session in tune. Back in the days when maybe one person (usually a fiddler) would bring an A tuning fork to a jam and tune to it, and then everybody else tried to tune to him, the group's tuning didn't stay there long. Soon, the group's pitch ran out of control and began to climb, and you'd get home (especially after a two- or three-day festival) to find that your banjo, guitar, or mandolin was tuned a fret or more above standard! I'm serious about that---I remember clearly getting home and discovering that my mandolin, tuned to "parking-lot standard" on Sunday afternoon, was a fret and a half above regular pitch! No wonder, I thought, it had been so hard to sing-- the songs were all 'way higher than usual!
So our electronic tuners help a great deal, not only with getting our instruments in tune in the first place, but also with tuning stability. However, keep in mind that the electronic tuner shouldn't be a substitute for your ear.
By that I mean that you shouldn't get fixated on the tuner. After playing your instrument for a year or so, you'll begin to hear the tuning better than at first, and ought to be able to make some adjustments without referring to the tuner. This is something that can be practiced: develop your "tuning ear". At home, use the electronic tuner to set one or two of the strings--- the 3rd string (G) and 4th string (D) are good on a guitar or banjo--- and then practice tuning the other strings to those. It'll be difficult at first, but you'll improve as you go. And then next time you're in a jam session, don't get glued to that tuner and tune and tune and tune your instrument while everyone else is waiting to pick. That's one time when electronic tuners are NOT a help. Use your new tuning skill to get your instrument in "pretty close" tune quickly, so that the jam can go on. Then, if your instrument needs more adjustments, it can be fine-tuned a bit in the break before the next song, and the next one, and the next one, without your taking up the whole group's time by trying to get it perfect.
The tuner can be hypnotic, but remember that it's not worth trying to get your instrument PRECISELY tuned to the tuner. After all, (1) the tuner's not perfect, (2) the other musicians' ears (and yours) aren't perfect, and (3) instruments don't note perfectly either, once they're supposedly tuned! Practice tuning until you hear the notes pretty well and can use your ear to promptly get your instrument "close enough" to being right in tune. That's a musical skill that really counts!