The metrology of measuring instruments is critical to any organization’s quality operations. Effective calibration of weighing instruments is the prerequisite for traceable and accurate weighing, covered under the company's quality management system. However, not all organizations have a thorough understanding of current metrological science. Calibration is more than simply placing reference masses on the weighing platform with the objective of assessing the deviation between the indication and the mass value of the reference. In fact, calibration is a process that establishes a relation between quantity values provided by measurement standards and corresponding indications, which is only complete if the contributing measurement uncertainties are taken into account. With regards to non-automatic weighing instruments (NAWI), the only global document is the EURAMET calibration guideline cg-18 "Calibration of non-automatic weighing instruments", which will also act as basis for the future development of a US calibration guideline. This white paper describes in detail the test procedures and measurement uncertainty estimation of the EURAMET cg-18 calibration guideline, highlighting laboratory and production area applications. Minimum weight is also covered, which defines the lower boundary of the safe weighing range. Weighing quantities within the safe weighing range guarantees compliance with the required weighing process tolerance.