what input pin is it using?

o ok i see thanks for that link one problem i can see is i am using an arduino uno and i will eventually need 3 hall inputs so how will i overcome that?

There's a delay(50) in the ISR. Not a good idea.

yes there is where it is blinking the led i dont actually need that led how can i get rid of that function as ive noticed if i remove void rpm_fun() i get a error