How to create a automatic weight calculation ?
Like this TEMPLATE ? (Copied from a other manufacturer's drawing)
I am not sure if this apply for NX9 but in NX10 it is done by using the mass system attribute (refer to https://docs.plm.automation.siemens.com/tdoc/nx/10
Here is a very good tutorial by Phoenix on how to setup it in drawing templates.
The best way to "Automatic Weight calculation" is with expression, as mentioned in the previous answer, to make it more efficient, make sure that, you use feature group concept, so that measurement goes to the feature group which is always comes after the body creation, if someone made any changes to the body, like add material using unite or subtract, the weight measurement gets adjusted automatically, since "measurement feature" is after the Boolean (or) edit feature.