Fox3snapshot:
My next question though is what altitude information is displayed on your TCAS display on the adjacent traffic as this once again could differ to what the ATC radars would be displaying if it is derived from the transponder/tcas equipment only based on 1013.
The only altitude information TCAS ever displays is that relative to the other traffic. The traffic symbol can have a 4 character tag; A plus/minus sign and 2 digits for altitude difference in hundreds of feet and an up or down arrow if it is climbing or descending more than 500 feet per minute. Once again, like the transponder, this is all based on a hardwired standard pressure altitude setting, so the pilots cannot stuff it up with an incorrect altimeter setting. If the aicraft are separated by by only (say) 100 feet, then that is what both aircraft will see in relative terms (100 ft) and you will see in absolute terms (eg. FL 249 and FL 250)
More info at
TCAS Symbols and some good pictures of a typical display during RAs down towards the end of
TCAS Displays
DD