GPS receivers add twist to hide and seek

“It just has a broad appeal,” he says.

The number of registered users of the Web site has doubled each year and now stands at 260,000, Mr. Irish says. He estimates that there are some 13,000 to 15,000 regular geocachers worldwide, who log about 65,000 finds a week from the more than 126,000 caches in 210 countries.

Mrs. Black has found more of those caches than any other player, becoming a legend in the geocaching community under her screen name, CCCooperAgency, also the name of her family’s insurance business.

Her determination to add to that number has taken the family, which also includes the Blacks’ three children, Lucy, 21, Craig, 13, and Nina, 7, across the eastern United States from Maine to Florida and as far west as Kentucky and Tennessee.

“I don’t do anything besides geocaching. That’s bad,” she says.

“You need to set up a clinic for Geocachers Anonymous,” Mr. Black responds.

• • •

For the Maryland Geocaching Society’s picnic, several new caches have been set up in the park and listed on the Web site. Many of the people at the picnic spurn the hot dogs and hamburgers for the chance to be the first to find the trove.

Mrs. Black joins Jane Nocera of Mohnton, Pa., her sister, Beverly Deysher, Molly Graber of Mount Joy, Pa., and her friend, Carl Horges, on the hunt.

In the woods about a mile from the picnic area there’s a cache with a cryptic clue — “The root says it all” — that players interpret as directing them to look for the roots of a tree.

The limitations of the GPS units — which indicate the direction in which to travel — now become obvious. Because civilian GPS receivers are accurate to within only 20 feet, when a geocacher gets that close to a cache the receiver’s display of distance and direction becomes unreliable.

Here today Mrs. Black, Ms. Nocera, Ms. Deysher, Ms. Graber and Mr. Horges is each carrying an individual GPS unit, and as they draw closer to the cache each is led in a different direction.

Some receivers direct their users downhill toward the roots of a large downed tree, and others uphill toward another large tree.

Mrs. Black heads for the downed tree. Ms. Nocera heads uphill, reaches into a hollow and pulls out a plastic container. It’s the cache they were looking for.

“When you see the big uprooted tree, where would you run?” Mrs. Black says when she arrives.

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