How to express the big and small notes in notation?

In the upper left corner, there is a symbol similar to 1=F, indicating that this piece of music is in the key of F. Judging whether it is major or minor can be determined by looking at whether the tonic of this piece is 1 or 6. The tonic is 1, usually in major and the tonic is 6, usually in minor. The score shows the beginning and end of the song. In major, it basically starts with 1 and ends with 1. Minor usually starts with 6 and ends with 6, but it is not absolute. It can only be said that most of them are like this, or basically. It depends on whether the tonic of the song is 1 or 6.

There is a symbol like 1=F in the upper left corner. If you look at the score, it is 1 as the main key, then it can be determined that it is F major.

If there is a symbol like 1=F in the upper left corner, and the score is based on 6, then it can't be said to be an "F key" strictly.

There is a relationship between the big and small sounds in the mode. This article explains:

The Relationship between Music Theory and Knowledge

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According to this article, if there is a symbol like 1=F in the upper left corner, then the score is mainly 6, which seems to be D minor.