What is the origin of each hand movement for each spell in the Harry Potter universe?
There is so much information on the Internet about each spell, and for each spell, you can find the way your hand should move while casting it.
However, I do not remember any professor specifying how to move your hand in the book, and in the movies, only when the students are taught Wingardium Leviosa in the first year.
Here's an example, one of the most remembered spells is the unlocking spell 'Alohomora'.
In the Harry Potter wiki, from one end, you can see a GIF of Hermione simply pointing at a door from the first movie, and on the other hand, you can see a drawing that they claim is the way you should move your wand while casting it. (If you think that this source is not reliable for that information, I'm sorry.)
Of course, the second symbol is from the computer game. Obviously, for the game, they would need to invent a specific motion for each spell.
So given that you don't really get any information from any platform (movies, books, games), where do people get this information?
