How to calculate tolerance in mechanical drawing.

I'm sorry to interrupt you, but you asked the wrong question.

You know the dimension chain. All three dimensions need to be marked with tolerances to form a closed dimension chain.

As shown in figure 1, if it is necessary to ensure the total length of 25 and 9, then 16 will be guaranteed as long as these two dimensions of the machined part meet the tolerance requirements;

Figure 2. If it is necessary to ensure the length of 9 and 16, the total length is also limited.

If you insist on finding out the tolerance calculation method in the tolerance book, no problem.

M=+0. 15

N=-0.28