In case of a tie, we take the score for the back 9 holes.
If those are tied then the score for last 6 holes on back 9, is considered.
If that is a tie then last 3 holes scores on back 9, is considered
If that is a tie then the score of Last hole on back 9 i.e. 18 th hole of the golf course is considered.

The calculation is always on the back 9 of the golf course. Irrespective of which hole the players teed off from.