Corvallis Rendering Co. is a plant that turns waste animal tissue into useful products. It purchases scraps from slaughterhouses, animals that have died from natural causes, spoiled meat from grocery stores, carcasses of dead horses and pets from animal shelters, etc., and turns them into valuable products like grease, tallow, and bone meal. One of Corvallis's biggest suppliers is Oregon Meat Packers, Inc. (OMP), which operates a beef slaughtering and packing house. OMP and Corvallis sign a contract under which OMP will sell all of its scraps and offal to Corvallis. The contract is a detailed agreement which is a standard form supplied by the Oregon State Meat Packing and Rendering Association (of which both Corvallis and OMP are members). It provides a number of terms and includes a merger clause. The contract provides that for each load of material that OMP sends to Corvallis, Corvallis will pay 27¢ per pound "provided that the protein content of the material is at least fifty percent (50%) protein, as tested on delivery at Corvallis's plant. If the protein content is less than 50%, Corvallis shall pay 24.5¢ per pound."

When OMP delivers several loads of material that test at 49.5% protein, Corvallis sends a check reflecting the 24.5¢ price. OMP argues that it should have been paid at the higher 27¢ amount, since trade usage in the Oregon rendering trade is that 49.5 percent is always rounded up to 50 percent. Corvallis insists that the parties agreed to the 50% number, not 49.5%. OMP seeks to introduce testimony by its employees of the trade usage. 

1. What are the arguments for each side on whether such testimony should be allowed?