For the most part, our questions use the measurement system that is widely used in the American system. Once in a while, we do get in questions that use measurement system that do not use American system; instead they use metric system used by British or India or other Asian countries.
We promptly hear from parents about this and they demand that we correct them and they lecture us that we are confusing their children.
We agree that it is a bit confusing. That admission aside, let us take a different perspective - your children are going to grow up to compete for jobs with children across the globe {if you haven't read the book The World is Flat, I highly recommend you purchase a copy or borrow from a library and read it}.
So, learning a metric system that is used in a part of the world that your child is likely to compete is not a bad thing, after all!. Did we devise our program intentionally for you to learn these new metric systems? No! But having encountered a different metric system in a few questions, it is not a bad way to learn a few new things! Is it?
After all, you are subscribing to a program being developed by a bunch of Americans with help from Chinese and Indians (who have lived in various parts of the Europe before arriving in America) and Hispanic Americans!