Regarding the Flight Level vs. Altitude readout for ATC’s;
The transition altitude is usually configured into the Radar Display Software (RDS).
The ATC sets the local QNH into the RDS.
The RDS displays all Pressure Altitudes above the Transition as they are received (1013.25Hpa), in Flight Levels.
The RDS converts all Pressure Levels that are below the (configured) Transition, to Altitudes.
Because the RDS and the Aircraft convert based on QNH setting, they both see the same value (if they are set to the same QNH).
ATC’s can test this by setting a “very” different QNH into the RDS and observing that only aircraft below transition will show the variation. (Do not do this at an operational position, or without warning other sectors on the same RDS).
Invictus