Help with shoot arrow block

Heya everyone, someone knows how shoot arrow block works? I have been looking for a tutorial everywhere and nothing :(

I have a system that detects player direction but when I want to shot an arrow in a direction is not the correct. I have testing the block and found that direction works with integer numbers? How I could set a direction work properly? Y between 1 and 2 are too much separated in degrees. Please help me :D