MJ
all the TCAS units I have used give way more errors than 30 degs
Mine is at least 30 degs off most of the time but a quick look at the compass give me the general direction of the traffic and where to look.
e.g. if i am on a 090 compass heading and the PCAS says i am on a 030 with traffic at to my left rear quadrant, i am gonna guestimate its at my left front quadrant between 360 and 90