Swift Dzire Vxi Mileage and odometer readings not in sync

The ride quality is good, ride is comfortable. But the problem I am facing is I get a mileage of 15-16 (full tank to tank). Whereas the fuel meter in the car is showing an average of 21-27!!!😲

When I brought this to the notice of the service centre people, they told me the meter was ok. One of them even told me that the mileage is calculated only when the car runs at a speed of 20 km/hr and higher. I was amazed at this because that doesnot represent a true picture of mileage at a bumper to bumper traffic. Now is my meter wrongly calibrated? Or is maruti presenting a positive biasness to the users?

Experienced people please help!!!

Final Words Car is good. Please improve on the faulty meter reading part and remove the positive biasness on mileage front.

Areas of improvement NA.

Style, Ease of driving, ComfortLatest updates missing as u get in a hyundai car, space less as compared to a Honda car