The structure, layout, examples, and writing strategy used in this manual make it simply the best calculator manual ever. I even use it when trying to learn how to use other calculators! I've added a few written notes in the scanned original copy, mostly regarding two issues: 1) The Sharp EL-506D is a slightly smaller version of the Sharp EL-557: all functions are identical and all buttons except one look identical, so you can use the same manual for both calculators. 2) Try the built-in power-on self-test - I have added a note about this interesting but undocumented feature in Appendix C.