Pound = lb. and Ounce = oz. Why?

This is one of the questions that kept me wondering, but not enough to actively look for the answer. Today, my RSS feeder found a short article by the World's Smartest Human Being, Cecil Adams:

"Lb." stands for libra, the basic unit of Roman weight, from which our present-day pound derives. The libra weighed a little under 12 ounces avoirdupois.

"Oz." stands for the Italian onza, ounce. It came into use in the 15th century. Ounce comes from the Latin uncia, a 12th, which is also the source of the term "inch."

Of course, in the end, it does not explain why pound comes from pondo while lb. comes from libra. I guess random accident of human decisions got stuck with us again.

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