Given the global economy of today, parts and tools are made and shipped all over the world. That there are different methods of measurement in various countries will have a serious impact on trade, and requires an agreed upon method of measurement or conversion. Consider a manufacturer in Europe ships a part to a North American warehouse. They may have checked surface roughness originally in Europe and cleared the part using Rz, but a check at a North American location later will likely use Ra resulting in a different number. Quality control engineers must use this information and make decisions regarding whether to accept or reject parts. There are methods of converting Rz measurements to Ra measurements and vice versa. Luckily, the Mahr surface roughness testers are able to provide measurements using both Rz and Ra algorithms, thus simplifying the process of conversion and re-testing.