In my limited experience, shm(2n+0) is not really worth the effort. It produces worse timing than Internet NTP over an IPv6 tunnel.
shm(2n+1) however provides much better timing than LAN local NTP even when tunneled over USB.
Gary will probably chime in soon with data points showing that I'm beyond wrong, so take this with a lot of salt.I don't use the PPS refclock.
You have got to love it when the unenclosed mail client refuses to learn reply to the list as first recourse.
