That will show just how much of a rise you've had (8)
I believe the answer is:
altitude
I'm afraid I can't even guess how this answer relates to the clue.
Can you help me to learn more?
(Other definitions for altitude that I've seen before include "Height above sea level" , "Lofty position" , "Elevation above sea level" , "Height (above ground)" , "Loftiness" .)