For calibrating, you want a stylus with a sharp but SOFT tip!
A typical iPad stylus is like using your thumbs to thread a needle.
That is an iPad stylus at the top of picture and the other 3 I have showing range from cheap to silly in price but note that those three have a sharp plastic tip.
After calibrating, you usually don't need that much precision so the iPad stylus will work or a fingernail is great.