final reserve fuel

Hi,

Could anyone tell me how the final reserve for jets is calculated?

I know it's the fuel to fly for 30 minutes at 1500ft AAL in ISA
conditions at holding speed... But what weight do you use? Do you
assume that contignency fuel is burnt (so gross weight = TOW - TRIP
fuel - ALTN fuel) when starting the 30' holding and is it 1500ft above
the elevation of the destination alternate or above the destination? I
checked it in 2 publications. They stated the opposite...

Thanks a lot and Merry Christmass, Happy 2005 and many great landings.

Tim