approached previously by both Harry Partch and Ben Johnston, and proposes the decoupling of interface and sound production as a way forward. The design and implementation of a software instrument and a hardware prototype are described, both using a simple API for variable tuning instruments. The hardware prototype uses physical computing techniques to control the tuning of a string with a servo motor, while the software instrument exists entirely in a web browser. Finally, potential algorithms for clients of the API are presented, and the effectiveness of the hardware prototype is evaluated by measuring its pitch accuracy.