The studs are sold as rough-cut lumber after emerging from the sawmill operation without further processing by SSI. Also, the posts require no further processing. The decorative pieces must be planed and further sized after emerging from the SSI sawmill. This additional processing costs SSI $100,000 per month and normally results in a loss of 10 percent of the units entering the process. Without this planing and sizing process, there is still an active intermediate market for the unfinished decorative pieces where the sales price averages $60 per unit. Provide details for the gross profit margin percentage method for allocating joint costs.