Some of the field types have an option to include or exclude zero values in the upper level accumulations. The following field types have this option:

For Weight Average fields, it is the field being weighted that is tested for zero values. For Ratio fields, it is the numerator that is tested for zero values

If the Include Zeros box is not ticked and the record contains zeros in the relevant field, then that record is excluded from the calculation of upper level record values.