BTIZ wrote:
ATC radar's (at least they used to when I was working them) show you on
"assigned altitude" when you are within +/-200ft

No, ATC radar shows what your mode C reports.


... so if you are assigned
9000 it will say "90C"... if you are still climbing to that altitude it will
say 90 "up-arrow" 87, or 8700 climbing to 9000 assigned.

You've mixed up two differnt things that are going on. What you are
talking about is the center. The center tag will often have your
assigned altitude shown similar to the way your type aircraft is shown.
Your actual altitude will always be shown. This way other controllers
can see what each aircraft is assigned. In the TRACON we don't show
assigned altitudes in the data block because we are much smarter and
don't need that crutch. Actually it's because the assigned altitudes
are constantly changing so there's no point in doing that.



the "traffic alert" on the ATC system is geared to the 90C, if you are at
9300 it will show 90 "arrow" 93 and if there is a traffic conflict at 10,000
it will "alert" the controller.

Center only.



Then he may "bust you", but if it's a momentary deviation and no other
traffic is involved, the controller may query and ask your altitude to
verify that his read out is correct. If you say, level 90, Then he may offer
up a new altimeter setting to you, or just tell you that he sees 9300, as a
hint that he is watching, or that you need to get it looked at. If your
altimeter setting is not set to "local", his computer radar will
misinterpret the altitude ModeC information from your aircraft.

Never admit an altitude bust. Just get back to your assigned altitude.