1/2off. My for-poll answer - tyco dead reconing gps chipset, inside their `development kit`. It works better in tunnels, underground parkings, between high building. Each stopping I'm surprised with no-drifting gps-cursor in the software. There is something to compare. My old BU-353 died this december. That was 3rd russian winter of its onroof lifetime. Unfortunately it knows everything, 3cm of pure ice, 15cm of heavy snow, each winter there were -30°C and less, carwashing, dirth etc.
<--Some photos are in `my photos`