How to Control the Force!
Fortunately, even though they were in New York, there were plenty of high-precision machine shops on the outskirts, along with many small workshops. Finding one wouldn't be a problem.
Wang Yue contacted a machine shop in New York online. After paying a deposit, he arranged to pick up the part in person, and the shop guaranteed it would be ready within four hours.
Wang Yue went to buy a circuit-board prototyping kit, soldered the circuit together, and finished programming it. He also found a usable data-source app online and modified it so Yin Guo could use her phone to monitor how much force she applied.
When the connecting rod for the cue arrived, Wang Yue fitted the circuit board and sensor inside it, then attached it to Yin Guo's cue.
Once Wang Yue had finished, Yin Guo eagerly took the cue and inspected it, then ran a simple test at home.
She gently tapped an apple on the table a few times with the cue, then set it down and checked the data on her phone. She found that the force readings barely differed.
Looking at the figures, she asked in confusion, "Wang Yue, is your gadget not working properly? Why is the difference in the force I'm using less than two newtons?"
Seeing that Yin Guo doubted him, Wang Yue said helplessly, "That just means you train regularly. The force you use doesn't vary much. If you don't believe me, stand the cue upright, put an apple on top, and weigh the apple. Then calculate the force, and you'll find it's about the same."
Yin Guo still wasn't convinced. Taking his advice, she tried to place an apple on top of the cue, but it kept wobbling no matter how she positioned it.
Wang