EXFO FTB -5240S/5240BP Optical Spectrum Analyzer - Manual (Page 320)

Managing Results
314 FTB-5240S/S-P/BP
Managing Markers

integrated power between the markers in dBm (when horizontal
markers are hidden)

for WDM, spectral transmittance and EDFA modes, power difference
between the traces (active against reference or input against output)
for both markers in dB (when horizontal markers are hidden).
As markers C and D appear on the graph, the power difference between
the markers (C-D) related to the horizontal markers will be displayed in the
marker toolbar.
You can also move the markers directly on the graph tab. Drag the marker
to the desired area in the display. You will notice that the corresponding
box in the marker toolbar changes according to the marker’s position. If
you want to set a precise value for the marker, simply enter it in the box.
Note: After using the zoom tools in the graph tab, you can only move the markers
again on the graph after deactivating the zoom. Pressing the arrow in the
zoom tools section will deactivate the zoom function.
Note: Markers A and B cannot cross. Displacing a marker over the second one
will cause both markers to move together.