1 TRIG LEVEL: When viewing a signal, you normally want the displayed trace to begin at a specific point on the input waveform. The TRIG LEVEL (Trigger level) lets you determine (adjust) when the display trace begins with respet to the input signal. For example if you are observing a sine wave, you might want the trace to begin at the positive-going zero crossing, the negative going zero crossing, or somewhere in between. The TRIG LEVL control lets you adjust this.
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2 The Coupling switch allows you to select AUTO (free running) where the displayed trace repeats at a rate determined by the Time/DIV control independently of the input signal. This setting is seldom used becauses it does not give a consistent display. You end up with a blur which is hard to interpret. The NORM position allows you to synchronize the display with the input signal as explained above. The EXT position behaves in a similar manner, expept that the display is now synchronized with a signal connected to the EXT TRIG input. If the EXT INPUT and the input signal are connected together, then the scope operates identically as described in the first paragraph above. The TV-V and TV-H are designed to synchronize the display with the vertical or horizontal synch pulses of a TV set.
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The SOURCE switch lets you determine whether the display is synchronized with the signal on Channel 1, Channel 2, the Power (Mains) line, or the EXT TRIG input.
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The VAR Sweep allows you to change the horizontal sweep rate to either the value set by the TIME/DIV, or a slower value determined by the position of the VAR SWEEP knob. WHen the VAR SWEEP Knob is in the "Cal" position, the sweep rate will be the rate selected by the TIME/DIV control. Otherwse it will be a lower rate as determined by the position of the VAR SWEEP knob.