It's an ICAO thing... In RVSM westbound is EVEN... in non RVSM the levels are all odd?
Non RVSM
W/Bnd.........E/Bound
FL280.......... FL290
FL310.......... FL330
FL350.......... FL370
FL390.......... FL410
FL430.......... FL450
RVSM Airspace
West Bound East Bound
FL280.......... FL290
FL300.......... FL310
FL320.......... FL330
FL340.......... FL350
FL360.......... FL370
FL380.......... FL390
FL400.......... FL410
FL430.......... FL450