Moving a slider to set the music volume or control the air conditioning is a familiar task that requires little attention. However, adjusting a virtual slider on a featureless touchscreen is much more demanding and can be dangerous in situations such as driving. Here, we study how a gradual tactile feedback, provided by a haptic touchscreen, can replace visual cues. As users adjust a setting with their finger, they feel a continuously changing texture, which spatial frequency correlates to the value of the setting. We demonstrate that, after training with visual and auditory feedback, users are able to adjust a setting on a haptic touchscreen without looking at the screen, thereby reducing visual distraction. Every learning strategy yielded similar performance, suggesting an amodal integration. This study shows that surface haptics can provide intuitive and precise tuning possibilities for tangible interfaces on touchscreens.