How would I measure the angle a basketball enters the rim during practice shots (without expensive equipment)?

Assuming I want the ball to enter the rim at an angle of say 45 degrees, I have no way of observing this on my own shots or even reasonably accurately on someone else's shots. I understand there are excellent tools available to help basketball players adjust the arc of their shots and improve their field goal percentage, but this equipments costs thousands of dollars, which I don't have. Any clever ideas on how to do this?How would I measure the angle a basketball enters the rim during practice shots (without expensive equipment)?
If you have even a cheap camera, you mount this on a tripod placed along the side of the field goal, focused on the rim. Have this on multiple exposure, making someone do the clicking.



Or by the use of the video of your cellphone, or videocam just let someone do the recording then replay on slow-motion.How would I measure the angle a basketball enters the rim during practice shots (without expensive equipment)?
a protractor