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Screen Zero controls
Below the button is an edit control to set the desired Screen Zero position. It can be set either as a percentage of full-scale, or, if your system is calibrated, in volts or arbitrary User Units. You select the entry/display mode via the Units button, midway down on the right side of the dialog.
For example, in percent mode (Units not depressed) if you enter 25 (and the Screen Zero button is active), the waveform display will be shifted down such that a point that was formerly at 25% of full scale will now be at zero.
Note that at high trace magnifications (typical in Histogram display mode) the little up/down scroll button steps will be too big... you'll need direct entry in such cases. (In Histogram mode the Y-axis is in percent, so you can enter those values directly.)
To the left of the edit control is a small Curs button. Clicking this (or using ALT+SHIFT+Z causes the edit control to take the true value of the waveform under the solid trace cursor. This is usually more convenient than direct entry if you want to examine fine details in the waveform.
Just drag the cursor to the location of interest and hit Curs; you can then increase the display magnification (PgUp) as much as desired. Otherwise, if the area of interest was not near true waveform zero, it would tend to be driven off the screen at high magnifications.
If the display shows multiple channels, they are all shifted by the same amount. You can click the small color button next to the solid cursor readout to select the channel you are interested in, before clicking Curs to capture a value.
The ALT+SHIFT+Z option is particularly handy when the Zero control dialog is not visible.
Screen Zero affects only the vertical position of waveforms on the screen; it does not change the cursor readouts, the Y axis, Trigger operation, nor the data saved to a file. It has no effect (and is disabled) in Spectrum, Spectrogram, and Pitch Track (Sgram/PT) modes.
Note that the state of the Zero toolbar button shows whether Screen Zero is active, but the button text shows if any Data Zero mode is active:
Screen Zero state and value are not saved when exiting Daqarta, to prevent possible confusion in the next session.
Zero=1 activates Screen Zero, Zero=0 turns it off, and Zero=x toggles between on and off.
ZeroScrn=25 sets the Screen Zero position to 25% of full scale if the Zero Units button is off.
If Units is active, this same command will attempt to set Screen Zero to 25 volts (or 25 User Units), limiting the value to the actual full-scale range as needed. You can use ZeroScrn=25m to set 25 mV (or 25 milli-units for User Units).
ZeroCurs= (value ignored) sets Screen Zero to the true value of the waveform under the solid trace cursor.
Note that attempts to use either command when disabled in Spectrum, Spectrogram, or Pitch Track modes will result in "Control disabled. Aborting macro."
Alternatively, you can read the current value in percent via ZeroScrn?%, regardless of the units mode. This is particularly useful for macros using Buf0-Buf7 arrays to display computed waveforms, where you want the screen position to respond to Screen Zero the same way in all modes.
See also Zero (Screen and Data)
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