It is ususual for the actual measurement error to be as large as 200 metres.
However, I have noticed that the measured GPS position sometimes wanders away from the correct position,
and then gets "stuck" maybe 200 metres away and it won't come back. Thats if I stand still. But then
if I walk around a bit, it will suddenly come good, maybe ten or 15 minutes later.
I used to get this often, when I got off a train. The GPS reading would overshoot the station, and stop
several hundred metres down the track. I was told that this was a "feature", to prevent the apparent
position of cars shifting while they were stopped at the traffic lights.