GPS Alert!

Scott F (
Thu, 19 Aug 1999 07:49:59 -0700 (PDT)

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West Wight Potter Website at URL
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I just saw this in this morning's USAToday.

Global positioning system adjustment set
Some guide receivers may be off

By Susan Decker, USA TODAY

Anyone using a global positioning system to figure out
where they are or where they are going should keep a
compass handy.

The system of satellites, run by the Air Force Space
Command but used by fishermen, hikers, truck drivers,
pilots and a lot of other people, is having a
scheduled changeover in dates. Most people won't
notice, but some users could find older systems
displaying the wrong date or even the wrong location.

It's like the Y2K bug, in which computers read only
two digits for the year and can't tell the difference
between 2000 and 1900. This is called an "end of week
rollover," and it was planned by the military.

The GPS system, which keeps time and pinpoints
locations with 27 orbiting satellites, was designed to
operate on a 1,024-week cycle - 19.7 years.

Like a car odometer turning over to 100,000 miles, the
GPS time system will revert to zero when the cycle
ends at 8 p.m. ET Saturday. The satellites send out
time codes, which receivers use to determine location
based on codes from at least three satellites. If the
receiver doesn't recognize the rollover, it might have
a problem.

The Air Force will begin sending rollover information
to the satellites today at 6 p.m. ET, and that could
cause disruptions.

The satellites and military receivers, which are used
for such tasks as finding bomb targets, are ready for
both the rollover and Y2K, says Capt. Jodi Unsinger at
Los Angeles Air Force Base, which is responsible for
the changeover.

Corporate users, such as United Parcel Service and ATM
machines, which rely on GPS for accurate time, have
checked out their systems, manufacturers say. The ones
that might have problems are those built before 1994,
when civilian manufacturers didn't always follow
military specifications to allow for the rollover.

In many cases, flicking the system on and off to reset
it will be enough to fix it, although some may need
software upgrades.

The U.S. Coast Guard's Web site, which is located at, has a list of
manufacturers to contact.

Joe Mercurio, a charter fishing captain in Key West,
Fla., says he isn't worried about his 10-year-old

"If it works, it works. If not, I'll have to go back
to the old way," Mercurio says. "A compass should
always be part of a boat, that's first. The GPS is
second. If your boat doesn't have a compass to start
with, you're in trouble."

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