SImply press the offset button at back of ROLLOVA, that can add diameter or radius of ROLLOVA to your measurement.

The ROLLOVA might have low battery given the description. We recommend you to replace the 1632 button battery. If the screen still not work after replacing batteries, please contact our customer support team.

The roller system is built with a certain fraction level to ensure it doesn't slip on most surfaces. But because the fraction between ROLLOVA's tire and surfaces could vary among different materials (e.g. glass, rough surfaces), it may give you the impression of not rolling smoothly sometimes.