Hope this is the correct sub-forum for this topic...
In the tutorial "Parallel to Serial Shifting-In with a CD4021BE" (which can be found here), the schematics given are wrong in that Q7 is mentioned to output (or pass through to the next shift register) the parallel input to the Arduino, while it should be Q8. Q8 should go to the input pin of the Arduino, not Q7.
That's also mentioned in the article, where the package of the CD4021B is given: "Q8 is the only one used in these examples".
It is, however, correctly drawn on the wiring diagrams: pin 3 of the CB4021B goes to pin 9 of the Arduino. And pin 3 is Q8...