I like puzzles - so I liked your game. Because there is no tutorial or guide: Figuring out the rules is the main puzzle to solve.
It took me a while (maybe 20 minutes) to solve level 0. After I understood that part of the rules the level 1-4 where easy. (30 seconds per level) Level 5 took me again 10-15 minutes (I need to figure out more of the mechanic). Level 6 again took me some time (Again more rules to understand.).
After that I had fully understood how the mechanics work - the remaining levels where then easy.
Maybe you should think about making the difficulty more balanced:
Give some more hints to figure out the rules. For instance:
- The area where you put the "operation" could just be a circle, so that it looks more similar to the operations in the bottom right area.
- Show a connection between the areas where the "processing" is done, so that it is clear how the flow is
- Create more complex puzzles, that are hard even when you know the rules