Many new melodic instruments use a touch sensitive surface with notes arranged in a two-dimensional grid. Most of these arrange notes in chromatic half-steps along the horizontal axis and in intervals of fourths along the vertical axis. Although many alternatives exist, this arrangement, which resembles that of a bass guitar, is quickly becoming the de facto standard. In this study we present experimental evidence that grid based instruments are significantly easier to play when we tune adjacent rows in Major thirds rather than fourths. We have developed a grid-based instrument as an iPad app that has sold 8,000 units since 2012. To test our proposed alternative tuning, we taught a group twenty new users to play basic chords on our app, using both the standard tuning and our proposed alternative. Our results show that the Major thirds tuning is much easier to learn, even for users that have previous experience playing guitar.