[time-nuts] GPS antenna with direction orientation?

[John Ackermann N8UR]

A couple of years ago I picked up a surplus Aeroantenna choke-ring GPS 
antenna that I think was intended for surveying use.  I finally got it 
installed today and noticed that it has an arrow on the bottom 
indicating that the antenna should be oriented with the arrow facing north.

I'm trying to figure out why an omnidirectional antenna should care 
about which way it is oriented.  The best I can figure is that perhaps 
it is for repeatability in surveying, so that any minor offset in the 
phase center would remain consistent when moving the antenna from site 
to site.

Does anyone have a better answer?

John