This is the User Manual for the TDS 520 and TDS 540 Digitizing Oscillo- scopes. If you are a new user, try the Tutorial section to become familiar with the operation of your digitizing Oscilloscope The Concepts section covers basic principles of the operation of the oscillo- scope. These articles help you understand why your instrument works the way it does. Use the In Detail section to learn how to perform specific tasks. See page 3-1 for a complete list of tasks covered in that section. The Appendices provide an option and Accessories listing, product specifica- tion, and other useful information.