The operator is used with the conversion factor to convert the unit of weight to the standard unit of weight (listed first in the grid).
* = multiply by the conversion factor
/ = divide by the conversion factor
For example, if the first entry in the grid is "pound", if you want to enter ounces as another unit of weight, then you'd enter " / " (divide) in the Operator field, and 16 in the Conversion Factor field, because you must divide "pound" by 16 to get one ounce (because there are 16 ounces in a pound).