Not using SI units as our only measuring system in America has become a burden on businesses, education and trade. Businesses often package items in imperial sizes, and slap a metric label on, mostly based on imperial units. The problem with this is that, when selling products outside the US, they have to resize items to rounded metric sizes. This creates added cost as they size items to both imperial and metric, vs just sizing them in metric sizes. Added manufacturing cost often means higher purchase prices. International trade does indeed have an effect on local state by state trade because of this added cost. Schools create confusion as students are taught to convert between different measuring units instead of using only one unit. Often there has been push back from politicians on subjects such as this saying that its not a big cost. But over time it will be a big cost. To both our children and businesses. This can't be ignored any longer