When adding markers to a graph, you can make one marker a reference and the others will be relative to the reference. For example, see three markers on the following graph. Right click on a graph to be able to add markers to a trace.
Right click on the upper left marker and select Reference Marker. Notice that marker indicates that is the reference. The upper right marker now shows as a delta from the reference. The lower left marker did not change.
By default, reference markers only show deltas on the same trace. To make all markers show as deltas for the given graph, right click on the graph and select Options, go to the Markers tab and select the Ref marker all traces option.
Once set, the lower left marker is now also displayed as relative to the original marker.