startRotation method
Implementation
void startRotation(Canvas canvas, Size size) {
  switch (gaugeOrientation) {
    case GaugeOrientation.horizontal:
      canvas.save();
      canvas.translate(size.width / 2, size.height / 2);
      canvas.rotate(RadialHelper.degreesToRadians(90));
      canvas.translate(-size.width / 2, -size.height / 2);
      break;
    case GaugeOrientation.vertical:
      break;
  }
}