This article is from the Apple II Csa2 FAQ, by Jeff Hurlburt with numerous contributions by others.
To check and fine-tune your joystick, run an Apple II joystick adjustment program such as the one on the TNILUTIL disk available from Ground or GSWV (see Q&A 001 in Csa21MAIN4.txt). If you get a range of 0-255 for Horizontal and Vertical with centers around 128 and both buttons work, the stick is properly adjusted and ready for use. If you can not reach extreme values (0 or 255), the stick will not work for some applications. For example, you will not be able to guide your worm in the game "Serpentine". By: Rubywand