Electronic tuners are a good way to get your horn in tune on one or two reference notes, but you can't stop there. Even on the finest professional horns, intonation will vary from note to note. The only way to play in tune consistently is to listen and adjust as you play. Developing this skill will improve your overall musicianship, whether you're playing a solo in a scholarship audition or performing with 300 others as a Marching Southerner!