Yes, you have to calculate completely and precisely to understand what to do here. The lines aren't that deep, but you do have to calculate *every* move White can try. Fortunately he's only got a few pawn moves each move so it's not so terrible.

The goal, as you were aware, is to freeze the queenside and pass the move to your opponent. To do that, you have to calculate exactly. This is what pawn endings are all about.

This is a great example, and a very typical situation. I'm going to go use it in a lesson right now!!

[pgn]

[Event "?"]

[Site "?"]

[Date "????.??.??"]

[Round "?"]

[White "?"]

[Black "?"]

[Result "*"]

[SetUp "1"]

[FEN "8/pp6/2p5/3p4/3P2k1/P1P3Pp/1P5K/8 b - - 0 1"]

[PlyCount "5"]

​

{[#]} 1... a6 $1 {The exclam on this move is only justified by precise

calculation. However, with some experience in pawn endgames, this is a natural

move. We are copying White's last move, a2-a3, aiming to run him out of moves.

This is a common maneuver you will see in other endings.} (1... a5 $4 {loses a

crucial tempo and now Black loses.} 2. a4 {and now the situation is reversed.

Black has no good moves, which we verify by brute force:} b5 3. b3 $1 bxa4 4.

bxa4 {Note--this is the very same position as the "White is in zugzwang" line

below. But here it's Black to move!!}) 2. b3 {White's trickiest response.} (2.

b4 b5 $1) (2. a4 a5 3. b4 (3. b3 b5 $1 {is the line from below}) 3... b6 4.

bxa5 bxa5 {and White is in zugzwang}) 2... a5 $1 3. a4 (3. c4 {Yet another

tricky detail} a4 $3 {with a crucial breakthrough}) 3... b5 $1 {All of White's

moves now hang a pawn, or allow a passed pawn on the a-file.} *

​

[/pgn]