First, get two tubes. Place a ball on one of the tubes near the side pocket. The second tube is 1-1/2 diamonds away with another ball on top of it. The ball on the slate is about a balls width from the tube. I like to place the cue ball a diamonds width away from the middle tube.
This is a good test to see how straight your stroke is and how well you can control it. I noticed on my first few attempts I had a tendency to hit the ball off to one side so the cue ball and dropping balls would miss the side pocket. Even in the video, you see it's not perfectly straight. You don't need a lot of speed, just hit a firm stop shot into the object ball on the table. Make sure you hit it hard enough so the tube won't affect the cue ball's travel path.
This is a nifty little tube shot I concocted while on vacation. It'll test the straightness of your stroke.
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