I recently connected a [GPS unit sold by Adafruit](http://www.adafruit.com/products/746) to my Raspberry PI and looked at the data feed. The data I'm getting for speed seems to be way off. My PI is stationary, but it always reports are moving at about .5kph. It will occasionally go up to 1.5 kph.

![enter image description here](https://i.stack.imgur.com/pjafL.png)

The Speed Err is reported to be +/- 19 kph! That seems a little odd. Do I just have a bad signal indoors or is this to be expected? Is there any way to correct for these wandering readings?