I visited Angus Johnson's Simple Sudoko web site:

http://angusj.com/sudoku/hints.php

and found some very helpful solution techniques, but I am confused by his Naked Triple example.

In his example he states that if there only 3 squares within the illustrated group that contain the numbers 1, 4 & 6, therefore the 1 and the 4 can be removed from the remaining squares in the group.

The illustrated group also has 3 squares that only contain the numbers 1,5 & 7. How do I know which set of numbers is the true Naked Triple? If I follow the same logic using the numbers 1,5 & 7, I'd remove the number 1 from the squares the example indicates I should keep.