Measuring instrument in shop are checked by deparment of weight and measures in every two years, why?​

The standard weights and meters scale for every two years because they may raise some errors due to regular use
The measuring device on regular and continous use may loose their standards and results in some error
The national standards body National Bureau of Standards & Metrology (NBSM) verifies the standard weights and meter scales for every two years
There are also some other factors which can contribute to bring error in the measurement of instruments

If there was no gravity then their would be no downword force on the football to have it return the the grownd, and if there was no friction (mainly air friction) then there would be no opposing force the stop the ball from moving through the air allowing the ball to travle ∞.