Pulsar Nav accuracy

Hello everybody

Somebody mentioned that deep space navigation using pulsars (and nearby 
stars?) could be accurate to within an astronomical unit.  

Thinking about it, I doubt that this accuracy could be achieved with 
distant objects alone. 

Problem is, we have to know the position of the objects in 3 dimensions 
and the measurement is unlikely to be very precise.  

Assume we know the pulsars' position to within 1/10th of a Lightyear 
(big if) and that no other measurement errors creep in (another big 
if). This means we know our spaceships's position to within 1/10th of a 
lightyear. 

Using many pulsars won't help that much. If you take N measurements, 
the accuracy of your result improves with the square root of the 
number. 700 pulsars will give an improvement by a factor of 1/26 [ 
1/sqrt(700) ] that is 1/260th of  LY or 1 1/2 lightdays - about enough 
to know in which star's system you are. 

Greetings