A02 just means that the automated station has a precipitation discriminator (can differentiate between rain, snow and unknown precip)
The 51006 group is the pressure tendency for the past 3 hours. The number 1 means the pressure has been increasing, then remained constant, or has been increasing and then increasing at a slower rate. The bottom line is that the pressure was increasing at a faster rate during the first period of the 3-hour interval than at the end of the 3-hour interval. This gives you an indication of the trend (in this case you could probably expect the pressure to remain constant or rise less during the next 3 hours).
The overall pressure change was 0.5 hPa.
hope this helps.
palgia