The +-4% tolerance is guaranteed for 5000 cycles (5000 'clicks'), then the wrench should be re-calibrated.

Calibration is a service we offer in our laboratories at the cost of 35€ plus shipping expenses (may vary depending on the countries) for the standard Giustaforza, while owners of the Giustaforza Professional have right to a total discount on the first re-calibration (it will cost 0€ plus shipping expenses.. may vary depending on the countries). 

After every calibration, the tolerance of +-4% over nominal value will be restored for other 5000 cycles. The wrench will return back to the owner provided with a calibration certificate.