Imho, heights are as useful for classification purposes as plies or number of moves. If 2 positions can be obtained from each other by reversible moves than their are equivalent in this HFZ (height-from-zero) metric.
Height of an opening


You appear to have forgotten to take your tablets.
Go and continue to eat your prawns, don't disturb serious guys!

The Alekhine's Defense must be crawling with them: 1.e4* Nf6 2.e5* Nd5 3. d4* d6* 3. c4* Nb6 4. f4 * dxe5* 5. fxe5*
8 in all!

You appear to have forgotten to take your tablets.
Go and continue to eat your prawns, don't disturb serious guys!
My apologies, I begin to see that you are seriously disturbed.

The Alekhine's Defense must be crawling with them: 1.e4* Nf6 2.e5* Nd5 3. d4* d6* 3. c4* Nb6 4. f4 * dxe5* 5. fxe5*
8 in all!
Actually, e4, d4, c4, and f4 have height 2. So, indeed, it goes quickly to the height 12.

Openings of height 2 are divided in 3 cases: 2+0, 1+1 and 0+2
2=2+0: Nimzo 1.e4 Nc6, Alekhine 1.e4 Nf6, Lundin-Mikenas 1.d4 Nc6, QP Indian 1.d4 Nf6 etc.
2=1+1: Symmetrical NLA and King's Indian 1.b3 b6 and 1.g3 g6 etc.
2=0+2: Réti QP 1.Nf6 d5 etc.

Hmm...
does a capture with a pawn counts as one or two?
Yeah, right, the capture with a pawn counts as 2 (taking + advance on 1 square)!

The Alekhine's Defense must be crawling with them: 1.e4* Nf6 2.e5* Nd5 3. d4* d6* 3. c4* Nb6 4. f4 * dxe5* 5. fxe5*
8 in all!
Actually, e4, d4, c4, and f4 have height 2. So, indeed, it goes quickly to the height 12.
Even 14, as dxe5 and fxe5 have height 2, as noticed by draconlord.

waitt so this is a method of determining a positions stretgh I still dont get it
It can be used to determine the amount of weaknesses in a position. In example, overextended pawns.

waitt so this is a method of determining a positions stretgh I still dont get it
Nope, that's rather to quantify how far an opening goes from the initial position in da middlegame. Though, as noted by Lokas, it reflects also the extension of pawn structures. Let's say the height 15=10+5 means essentially that white pawns are more developped.

waitt so this is a method of determining a positions stretgh I still dont get it
Nope, that's rather to quantify how far an opening goes from the initial position in da middlegame. Though, as noted by Lokas, it reflects also the extension of pawn structures. Let's say the height 15=10+5 means essentially that white pawns are more developped.
but what would be blacks hieght then when you say 15=10+5
This is a concept related to DTZ (depth-to-zero) metric in da endgame theory. The height of an opening is a number of irrevirsible moves (basically, takings and pawn moves) in it. Initial 2-squares pawn moves have the height 2. So, for example, the height of Ruy Lopez is 4.
Heights are useful for classification of openings and all chess positions. They determine how many exchanges were made and how far pawns advanced. The total height of the final position with only 2 kings is about 90.
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I count the height of castling as 3 cuz the king and 2 rooks lose an ability to castle the 2nd time. So, the castling is an irreversible move of height 3 for me. The height is also naturally divided in 2 parts (for white and for black).
Height h of the traditional line in Najdorf:
1.e4 (h=2+0) c5 (h=2+2) 2.Nf3 d6 (h=2+3) 3.d4 (h=4+3) cxd4 (h=4+5) 4.Nxd4 (h=5+5) Nf6 5.Nc3 a6 (h=5+6) 6.Bg5 e6 (h=5+7) 7.f4 (h=7+7) Be7 8.Qf3 Qe7 9.O-O-O (h=10+7) Nbd7 10.g4 (h=12+7) b5 (h=12+9)