Taking degrees of freedom from uncertainty into minimum weight estimate for analytical balances

There is a great need to weigh very small mass samples in analytical balances due to cost reduction and sustainability requirements so weighing results should accomplish the accuracy requirements in selecting and quality checking tests. The minimum weight is an important balance performance requirement for small mass weighing and is defined as the load for which the relative expanded uncertainty is equal to the accuracy requirement. When "uncertainty" of uncertainty of repeatability is regarded in minimum weight determination, the lack of information about degrees of freedom can cause an underestimated value. Thus, here is shown a modified equation for minimum weight calculation which regards the uncertainty of repeatability uncertainty to take account of the degrees of freedom. Besides, it is developed a simple approximated equation for minimum weight calculation.