Ao Oni Calculation Puzzle

The calculation puzzle is exclusive to Ao Oni Version 5.2.
The puzzle is fairly straight-forward, but is slightly similar to the piano puzzle.

Once you have the diary and inserted the ripped page,
you will be presented with a math expression but the solution isn't immediately obvious.
The solution to this will be asked for later on.

There is a table in the basement that gives a hint of what to do with the puzzle.

If you know your addition pretty well, this equation is not actually true,
unless you look at it from a different perspective.

Let's look at one real instance of the puzzle to see what's going on here.
(To those that got these numbers, consider yourself lucky).

As we can see, the diary is asking for 9091 + 6128.
We should consider the table's equation being not true.
This means the solution the diary is asking for is also not true from this perspective.
Let's rotate the diary 180°.
To do this practically, you can either tilt your head to see what the number should be like,
or you can write the expression on a piece of paper and rotate it.

Below is what it should look like.

Now that the expression is laid out like this, we can attempt to solve.

Now we have the number, but the place we need to put the combination into will say it's wrong.
So to get the actual right number, we need to rotate the whole thing again by 180°.

Below is what it should look like now.

Now we have the right number: 5286.

You have now solved the calculation puzzle.

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