A little math question I have...?

After escaping from the earthquake, flood, and tornado which had afflicted his city, all the poor shopkeeper could dig out of the rubble of his store was four pairs of weights and a balance scale. Fortunately, he was good at math, and found that he could weigh anything from one pound to 170 pounds with the four pairs (please note: pairs, not individual weights). What were the four pairs of weights?