Yea, I was surprised to learn about the margin of error too, but there variations with blood glucose within the body too, and the meter is calculating plasma glucose from a whole blood sample... so there is some room for error.

I guess it surprised me because I expect medical devices to be so precise, but they are tremendously accurate when you consider that not so long ago people had to test their urine to determine if their blood sugar had been high. That, and they're built to be affordable...