Question: **Context**

I'm learning how to use Google's - GTFS-realtime 

The timestamps that are supplied by a service adhering to this standard are described on this page: <https://developers.google.com/transit/gtfs-realtime/reference>

Part of the instructions include this sentence: 

"To avoid time skew between systems producing and consuming realtime information it is strongly advised to derive timestamp from a time server."

**Steps Taken To Understand**

1. I looked over the wikipedia page on time servers - <http://en.wikipedia.org/wiki/Time_server>

**Question** 

1. Can someone clarify what this instruction means in practical terms?

Answer: 
Suppose that your application is running on multiple machines. Some event occurs concurrently (at the same time) on two or more machines. If the machines time is **not** synchronous (machine 1 says 01.09.2013 **08:00:00.000** and machine 2 says 01.09.2013 **07:58:45.123**). The events will not have the correct appearence in your log (or display, or whatever)!

If you ask a time server for the timestamp, then both events will have **the same timestamp** respectively all events (no matter on which machine) will have the timestamp from the **same source**! Timestamp could be important (event order, priority, and so on).
In practical terms, what this means is whenever you want to get a timestamp for use in your application, instead of using your own copmauter's timesatmp, you should get it from a time server on the network. To set this up , you can read this: <http://www.pool.ntp.org/en/use.html>