The TEKTRONIX 2445 and 2465 Oscilloscopes with Option 05 (TV Option) have additional hardware and software features to simplify triggering and viewing of television signals. The option adds TV (back-porch) clamp circuitry to the Channel 2 input and TV trigger coupling modes are provided, allowing a user to select either horizontal or vertical sync pulses to obtain horizontal-line-sync or field-sync pulse triggering. This option permits the user to trigger on a specific line number within a TV field and provides sync polarity switching for either sync-negative or sync-positive composite video signals.