Originally Posted by JCL

OK, let's do this again. This time I will post what the manual says, instead of going from memory.

1) Park the vehicle on a level surface
2) Switch the engine off after it has reached operating temperature
3) After approximately 5 minutes, pull the dipstick out and wipe it on a lint-free rag
4) Etc.

If your vehicle is cold, your reading will be incorrect. If you let it sit for an hour or two, all the oil will drain down to the sump and it will be similarly incorrect.