換球時機 - 網球 Tennis

國際網總(ITF)的網球規則有一項和換球有關，但是我看不太懂

After an agreed number of games, in which case, the first ball change in the
match shall take place two games earlier than for the rest of the match,
to make allowance for the warm-up. 我看不懂這段


A tie-break game counts as one game for the ball change.
A ball change change shall not take place at the beginning of a tie-break
game. In this case, the ball change shall be delayed until the beginning
of the second game of the next set. 這部份我看得懂，供參考用


有沒有人可以解釋一下呢？
謝謝！！

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