The Sonic is an “audio only” vario intended to be mounted on your helmet. It has been especially designed for the mininmalist pilots who want to enjoy free flight with the minimum of technology and for pilots that want a reliable back-up instrument for cross country and competition flying. It is also great for coastal soaring, where an altitude indication is of little importance. The Sonic is an “audio only” vario intended to be mounted on your helmet. It has been especially designed for the mininmalist pilots who want to enjoy free flight with the minimum of technology and for pilots that want a reliable back-up instrument for cross country and competition flying. It is also great for coastal soaring, where an altitude indication is of little importance. Features: Automatic scale indication Optional sink tone/alarm Internally adjustable volume and sink tone threshold Sink tone threshold: 20-1000 fpm (0.1 - 5.0 m/s) Weight:1.7 oz (46g) Dimensions: 3-1/2 x 1-1/2 x 3/4in. (89x35x18mm) Battery life: +/- 200 hrs. Battery type: Lithium CR2450 (3v/500mAh) Battery, self-adhesive attachment velcro and carry bag included