[gentoo-user] /etc/init.d/: ntpd or ntp-client?

[Stroller]

Hi there,

I just logged into one of my machines that has recently been powered  
down for a few days - not a terribly common occurrence with my servers  
- to find a date of January 30th showing.
I used to run ntp-client, but AIUI adding this to the default runlevel  
only sets the clock once at boot up. Of course the problem with that  
is that the computer's clock can become inaccurate if the spring  
tension is weak, as is obviously the case in my older PCs.
So a while back I changed /etc/runlevels/default so that ntpd is  
started instead.
I understood that ntpd was not only a server for my LAN (a facility I  
don't use) but that it would also periodically check the time with  
upstream servers & keep the machine's clock in constant sync.
So when I found the clock to be a week out of date I checked that ntpd  
appeared to be running (it was) and restarted it. The date remained  
the same. Stopping ntpd & starting ntp-client corrected the date  
immediately.
Before I do any investigation, can someone tell me if my understanding  
so far is correct? Is ntpd supposed to keep the machine's clock in  
constant sync, or is it only (say) a server to offer the date to  
clients? (depending upon the clock being set correctly by other means)  
I thought I had configured ntpd with upstream servers separately from  
ntp-client.
Stroller.