If you are a multi intrumentalist finding a single tuner that works for everything you play. Every instrument responds differently to tuners and a lot of time tuners can't pick up the intricacies of tuning. Enter the Snark SN-11 clip on tuner that fixes all of these issues.
If you have ever played with a live piano we have all encountered that moment when the piano is anything up to a quater tone flat. Before you could tune by ear but that doesn't guarantee perfection. The SN11 does fix this issue however as you can set the relative frequency of the tuner to match the piano making tuning a dream.