Hi there Geoffrey!
Don here from Shopify!
That's a really interesting idea though not something that is currently possible using Shopify. :)
What you can do is to enter the weights of your products when listing them and then manually enter the weight of any packaging you need to use in your settings > shipping menu.
These weights would then be combined by the admin to generate the total order weight which would be used when providing shipping rates at checkout to ensure the best match for rates.
Feel free to reach out to us anytime using our support site if you have any more questions. :)
All the best!
Thank you, Don. I know about the method you've indicated. It just requires a lot of work weighing everything and still is prone to error. It's surprising there is no App or functionality for a postage scale. It seems like such a basic need. Perhaps there will be before too long.
I apprecaite your help.