The J7 supports dual-band connectivity.
Before mounting the device, you must initialize it to set the measurement units and calibrate it for your specific bike. YouTube·WorldofTech Cyclocomputer Echo J7 Manual
Note: If your unit says "Auto," you do not need to press Start/Stop; the device starts when the wheel turns. The J7 supports dual-band connectivity
Problem: The unit reads speed but not cadence (or vice versa). Fix: Re-align the magnets. The magnet must pass directly over the sensor's "sweet spot" (marked by a small triangle on the sensor casing). Problem: The unit reads speed but not cadence
If you skip this step, your speed and distance will be wildly inaccurate. The refers to this as "Wheel Circumference (cm)."
But a powerful computer is only as good as its setup. Here is your official manual and operational guide to getting the most out of your Echo J7.