I think he means if he goes somewhere that is starting out at 2000'... like on a mountain or hill or something...
You shouldn't have to re-calibrate it. The calibrations are for compass and inertial movements/position. Height is determined by the sensors on the bottom of the Spark. They only measure from the starting point (AGL, Above Ground Level). So if you are at 0' when you start and go up 400'...then you are at 400'. But if you are on a 2000' hill and go up 400', the Spark will only register 400' even though you are technically 2400'.
I hope that helps.