The trick is in the coins’ metallic body – a mix of copper and silver that makes them much less sturdy than coins from present times. Medieval coins were easily frayed by everyday use, and by studying the degree of this wear and tear, Gullbekk was able to come up with rough estimates of how many hands the coins have seen in their lifetime.
Gullbekk explains that if one knows the time period certain coins were used, one can make a well-informed guess of the coin’s circulation velocity in the years it was used as currency.
I bet this trick would work for the period of Anglo-Saxon coins in England, as the government was apparently successful in forcing everyone to turn in their coins to be melted-down and re-struck periodically. Thus, when we do find coins from a particular period, it's in hoards whose age can be estimated fairly precisely. You could take those coins and have a very reasonable estimate of their life in circulation. (The only problem is the relative rarity of such coins, since -- as mentioned -- the government was fairly successful at collecting up old coins and melting them down.)
H/t: Medieval News.