Divided into 3 groups:

1、2、3、4

5、6、7、8

9、 10、 1 1、 12

1, 2, 3, 4 and 5, 6, 7, 8 scales

If the weight is the same, the problems are 9, 10, 1 1 and 12.

Represented by 9, 10 and 1 2.

If so, the problem is 1 1 or 12. If it is 1 1 and 1, it is 12. The difference is 1 1.

If not, the problem is 9 and 10. If you use 9 and 1, it is also 10. The difference is 9.

1, 2, 3, 4 and 5, 6, 7, 8 scales

If they are not of the same weight (assuming 5, 6, 7, 8), it means that the problem lies in 1 to 8, or 1, 2, 3, 4, or 5, 6, 7, 8.

Use 1, 2,5 and 3,6,9 (9 has been proved to be normal).

If the weight is the same, it's either 4 light, 7 heavy or 8 heavy, and then 7 and 8 will come out, so I won't go into details.

If 3, 6 and 9 are light, it is obvious that the problem lies in 3 or 5. Find a standard object, weigh it with any one of them, and you will know the answer.

If it is 3, 6 and 9, it is either 1, 2 or 6.

Then 1 and 2 are the light ones, and if they are the same, they are 6.