I just found an .exe (Windows, PC) program that makes aligning your tonearm and cartridge very easy. It creates a printout for your tonearm. It's on this page:
http://www.conradhoffman.com/chsw.htm
Click the third link, "Custom arc template generator for phono cartridge alignment (also prints strobe disks)"
Discussion on this page:
http://www.vinylengine.com/turntable_forum/viewtopic.php?t=16849
My homemade tonearm is 297 cm long in effective length. I had to do a little trial and error to arrive at the correct effective length in the program, but once I did, wow, so easy to print and use! For now I'm using "Loefgren A" (which is also known as Baerwald). Enjoy!