Hi all.
The 818.0 height is the height of the plans measured from the floor of the ground level to the floor of the platform at the top of the structure. The floor of the ground level is 11.5 m. above the Dubai Municipal Datum and 15.25 m. above the raft. The DMD is some 1 meter above sea level AFAIK.
The official measure when it is completed could be :
1 - 818.0 - as the plans say.
2 - 819.1 - from the floor of the ground level to the top of the handrail around the top platform - a permanent part of the structure.
3 - 824.0 - from the floor of the concourse level to the floor of the top platform. There is 3 entrances on different sides of the structure all at different levels. One is at level 1 - 4 m. above ground level, another is at the ground level, and the other is at the concourse level - 6 m. below ground level. The grade is at those levels for each so the concourse level could be a legit starting point for the height.
4 - 825.1 - from the floor of the concourse level to the top of the handrail around the top platform.
I think sticking to the numbers in the plans is prudent for the time being.
Current height is 656.1 m - floor of the ground level to the top of the second section of tier 19.