Signal subtraction
The signal subtraction tool is activated by pressing the 'Signal subtraction' button in the toolbar or via the menu 'Display / Signal subtraction'. The subtraction tool is displayed at the top of the waveviewer window.
![](../Jpeg/Waveviewer_Subtraction02.jpg)
Subtraction tool is active, still empty
Click on 2 signals to copy them to the subtraction area. The first signal will be colored red, the second clicked signal is green. Both selected signals are displayed on top of each other. The green signal is subtracted from the red signal and the results, the subtraction signal, is displayed just below both selected signals.
Delay or advance the second/green subtraction signal up to 500ms using the slider bar just below the subtraction signal.
Check 'Same as source signals' to set the scale of the subtraction signal equal to the red and green source signals. You can modify the scale (or range) of a signal by moving the mouse button over the signal and by using the '+' and '-' keys, as described in Display of waveform.
Press the 'Clear signals'-button to erase the subtraction selection and start a new subtraction.
When finished, close the subtraction area by clicking the 'Signal subtraction' button in the toolbar or via the menu. If the subtraction channels are not cleared, these channels will remain coloured red or green.
![](../Jpeg/Waveviewer_signal_subtraction01.jpg)
Subtraction tool at the top, pressure signals P1 and P2 are selected for subtraction
The subtraction window can be used to determine the period before and during use of adenosine, to calculate the fractional flow reserve (FFR).
![](../Jpeg/Waveviewer_no_adenosine.jpg)
No adenosine
![](../Jpeg/Waveviewer_adenosine.jpg)
Using adenosine