Here, we will explain the example of advanced class one by one for your better understanding.
*Example
*Answer procedure
1.Beginner class : B Technique 1 (Fill in the sideways) to B Technique 3 (Hidden skewer)
After reviewing by beginner class
2.Intermediate class : I Technique 2 (With number and scrutiny)
1.Find 12-12 in area C, which changes row 8. F(7d) should be 1.
2.Find 7 for row 6 is only H(6g), therefore H(6g) should be 7.
3.Find 348-34-348 in column b, which changes 158 to 15 in B(6b).
After reviewing by Intermediate class
3.Advanced class : A Technique 3 (4 cells decision / 4 areas) "X wing"
"X wing" :
Watch A(3c),G(3i) and H(6i), you will find 28-25-58 pattern.
B(6c) should not be 2,5,8 i.e. 1
If you understand this , you may solve the rest.
This example takes 0.83 seconds at advanced level in Sudoku Solver.