Originally Posted by
khorton
Keep in mind that the resolution on that TCAS altitude display is only 100 ft (ie. ±50), and there could be up to 50 ft error in the baro altitude that feeds the TCAS on each aircraft. So, if it shows +200, with worst case stack up of errors the actual altitude difference could be as much +350, or as low as +50.
Not quite.
While your TCAS displays relative altitude in 100s of feet, that has been calculated from two transponders that are (nowadays) almost always sending altitude in 25 foot increments.