Metric is more accurate.distance travelled by light in absolute vacuum in 1/299,792,458 of a second the international inch is defined to be exactly 25.4 millimeters Read that 2nd link for what it was based on before metric knocked some sense into them. Something based on the speed of light is generally going to be more accurate, and make more logical sense, than something based on the average man's thumb width. Don't agree, imperial is as just as accurate.