Building number memory retention. (exercises)

To become a good sudoku number player you must be able to "hold" a number(s) in your mind.

H9 Three-Grid Excercise

Below are three 1 to 9 number grids. Each grid is missing two numbers - determine the missing numbers - making a mental note of them.
3
1
9
4
5
7
8
6
5
9
7
8
1
2
3
4
6
4
8
2
7
3
1
9

Now proceed to the three below grids. Determine the missing numbers in each - making a mental note of them, also.

4
5
9
8
1
7
2
3
3
1
4
5
6
9
7
8
8
6
7
3
2
9
5
1

Now recite all the above grid numbers. Repeat this process until you can. (mentally repeating and recalling the numbers)

Ok, once able to do the above - proceed and determine the missing numbers in the three below grids.

5
4
3
6
8
9
2
1
2
3
4
9
6
5
8
5
1
2
7
3
4

Ok, now recite all the above determined missing grid numbers. Repeat this entire process on this page until you can.

Can you recall all the below missing numbers?

3
1
9
4
5
7
8
6
5
9
7
8
1
2
3
4
6
4
8
2
7
3
1
9
4
5
9
8
1
7
2
3
3
1
4
5
6
9
7
8
8
6
7
3
2
9
5
1
5
4
3
6
8
9
2
1
2
3
4
9
6
5
8
5
1
2
7
3
4

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