      context.save();
        context.strokeStyle = 'rgba(0, 0, 0, 0.1)';
        context.beginPath();
        context.arc(polygon.x, polygon.y, polygon.radius + DEGREE_RING_MARGIN - TICK_WIDTH, 0, Math.PI*2, false);
        context.stroke();
        context.restore();
    }

    function drawTrackingDial(polygon) {
        context.save();
        context.shadowColor = 'rgba(0, 0, 0, 0.7)';
        context.shadowOffsetX = 3,
            context.shadowOffsetY = 3,
            context.shadowBlur = 6,
        