Dead Reckoning feature lacking in Nuvi 3-- series?

I was reading some reviews of the Nuvi 350 and 360. A few reviewers
mentioned the lack of dead reckoning capability.

Can someone explain what that feature is and how its absence would
affect the day-to-day use?

Thanks
Ken K

Dead reckoning is the ability to continue auto-routing if the unit loses
satellite lock, say when you enter a tunnel. It requires a physical
connection to the vehicle's speedometer system. I don't know the Nuvi
units but the comparison that I do know is the difference between the
StreetPilot 2610 and 2650.

Ivor

Ken wrote:

Based on my exprience with nuvi 350, there's some kind of poor man's
dead reckoning feature in the SW as the unit shows a moving map in most
of Boston's Big Dig tunnels, even in the 1-mile long Williams Tunnel to
Logan, but somehow not in the old Callahan Tunnel; it's puzzling, but
that's what I've seen many times... I don't believe there are any
transmitters in the tunnel, so the unit must assume that the speed will
not change for some time...

z.entropic

z.entropic wrote:
Thanks.

Ken K

I googled dead-reckoning and found several items.
Among them is this. I learned something too. . .

http://en.wikipedia.org/wiki/Dead_reckoning