Forget the maths, the answer is defined....
LARS = Lower Airspace Radar Service.
Lower Airspace (in the UK) = up to FL100
Simple answer for upper limit (unless regulated airspace gets in the way)
Lower limit is not defined, but obviously you need to be in cover. Service may be limited at low level and RAS (available for IFR flights only) may take terrain clearance issues into account, establishing a safe minimum altitude below which that service is not available
(All subejct to locally specific limitations... but this is the basic principle)
Last edited by Pierre Argh; 11th September 2005 at 15:40.