If your device iGS618 / iGS620 is showing inaccurate distance, pls check the following tips:

1. If you haven't equiped a speed sensor.

In this case, the distance was measured by GPS signal.

The speed will be affected when riding under circumstances with weak GPS signal, like in tunnel, mountainous area or indoors, or or near building, which will impact the distance value.

To avoid the difference, it is recommended to equip a speed sensor.

Refer to the article : Is it necessary to equip a a speed sensor?

2. If you have equiped a speed sensor,but it still show inaccurate distance.

You may need to refer to the wheel chart to reset the wheel size for your device iGS50.

Refer to the article :Tire Size Chart