It's unlikely calibration is the cause of your problem, however, in the case where you feel like you've tried everything it might be a good idea to do a factory reset of the sensor's settings.
To initiate a factory reset, follow these instructions:
1. Turn on your device and connect it to your iPhone
2. Once the device is connected, from the home page press the connect icon in the top left hand corner.
3. Press "Configure FLEX"
4. Now here's the tricky part that is slightly hidden, repeatedly tap the FLEX device image (red zone) for approximately 15 seconds, you'll need to tap quite fast to trigger the hidden reset feature.
5. Press "Reset"
6. Wait for the device to reset and disconnect
7. You're good to go!!!