Originally Posted by
DaveReidUK
The basic ADS-B data that most of them supply to FR24 is timestamped by using the PC's clock. We all know how accurate those are.
Most modern Internet-connected PCs should be synched via NTP; my laptop claims it's within 25ms of the half-dozen NTP servers it's listening to. But, yeah, the XP machine at work only seems to sync every few days, so it diverges quite a bit in that time.
I know ADS-C has a timestamp, but I think you're right that ADS-B doesn't. Since it's immediately broadcast, you know the time it was sent when you receive it... there's no delay from sending it through ACARS. My ADS-B receiver is down with a bad PSU at the moment, so I can't check how it's timestamping the messages.