The Korg CA-30 is a small and portable digital chromatic tuner. This is quite a popular one as I've seen and used them all over the place. It has pretty much everything you'd look for in a tuner and is quite inexpensive, making it the perfect choice for players on all levels. The tuner is probably best used with guitar and bass guitar, but suitable for stringed instruments and electronic ones as well. The tuner has a 1/4" input for plugging in your instrument, as well as a built in microphone for acoustic instruments. You have the option of sounding a note or tuning to the screen and LED lights. You also have the ability to set the calibration if you don't want to tune to A 440, which is nice and something you won't find on all tuners. I don't know exactly what type of battery this runs on, as I don't personally own one and haven't ever had to switch it out. As far as pocket sized tuners go, you aren't going to find many that are better than the Korg CA-30, as it's got all the features you'll need at a price that doesn't get much cheaper. Korg is of course a huge company who can afford to do this, but it's nice that it's still a high quality tuner that has a good amount of features and flexibility to work with. This is probably the tuner that I've seen most out there in terms of tuners of this size, and it's really hard to argue with the logic of getting one of these. In fact, I'd highly recommend all players in the market for a tuner like this to scoop one of these up, as you aren't going to find a better deal on a tuner...