I got this from this site:...

I got this from this site: http://goldoz.com.au/487.0.html

Fortunately most miners submit to a canned format of calculating cash costs according to a standard (non-GAAP) implemented by the Gold Institute (GI) back in 1996. Prior to this standard gold miners were very creative and non-uniform in how their expenses were presented to investors. And while not all miners submit to today?s standard, or comply to a tee, the GI-coined ?Production Cost Standard? has since become a relatively uniform metric across the industry.

According to this standard, total cash costs are calculated by adding cash operating costs (direct mining expenses, stripping and mine-development adjustments, third-party smelting/refining/transportation costs, and then adding back byproduct credits if applicable) to royalties and production taxes. This number is then divided by total ounces produced to get a per-ounce figure.

So silver by-product is a reduction in the cash costs.