Is there a delay onscreen?

[DavyF]

I live twenty miles from Belfast's two airports and ten miles from Newtownards airport, so there is a lot of aircraft activity. What time difference between a plane flying over my house and seeing them on the map? I have been trying to follow some of the aircraft I see but they never appear to match what I see on screen.

 

[Stealth]

I believe that most public tracking sites put in a small delay. It limits SAMS targeting opportunities
It may also be the type of traffic, not all light aircraft carry ADSB out equipment.