The meterics that account for economic activity will place a very low one on labor with a very low hourly rate.

AFAIK, Slaves would be categorized as capital expense, which is different than labor and would use a different measure for economic output.

Who cares how you classify the expense. They are talking about what percent of goods/services in our economy come from prisoners. It's negligible.

When slavery was a thing It was not negligible. It made up a good portion of the southern economy.

How do you quantify the goods and services that come from prisoners? It's not like they're stamped with (made in prison), but more likely would be marketed as (made in US).

Are you honestly suggesting that a large percentage of goods/services in the US are provided by prisoners or are you just arguing for arguments sake?

I doubt 1 in a million products are made by prisoners.

I was honestly curious how you might quantify that.