To ensure that your weighing scales or balances are weighing correctly we recommend that they are checked with calibration weights regularly. The frequency of the checks should depending on how important the measurement is to your product or process and what the implications would be if the weighing equipment was out of tolerance. You will probably have a weighing company calibrating your weighing equipment six monthly or annually but this only ensures that the scales are correct at the time of certification but if the weighing results are important to you then we recommend additional checks to ensure that any damage or a fault has not caused an calibration error. Even a poorly fitting protective cover can cause a significant weighing error that may not be obvious without checking with calibration weights