Some planetary scientists had previously suspected that the age estimates produced by counting small craters could be off by as much as a factor of 1,000. "We have found it's within a factor of two, which sounds pretty good to planetary scientists," Hartmann said. "It really allows us to sketch out the overall history of the Martian surface."
A factor of two means that if crater counting shows a feature was formed 20 million years ago, it's very likely to be at least between 10 million and 40 million years old.
"Whether it's 10 million or 40 million, that's still incredibly young on Mars," Hartmann said. "It's within the last one percent of the planet's history, and that's what's important. You don't want to go around saying there are features formed by water within the past 10 million years and then discover they are billions of years old."

There are for example water related landforms that occur inside geologically old terrain. But were these landforms created in the ancient period when the terrain was created or later?
This more accurate crater counting technique might help with that. Some interesting examples are in regard to the sulfate and phyllosilicates (clays) seen with the current Mars orbiters. These deposits frequently are seen in older terrain. This technique might be able to determine if the deposits are the same age as the old terrain or yournger.

Bob Clark