Stacking traces

Function overlayTraces(graphName, overlayPoint)
	String graphName
	Variable overlayPoint
	
	if (strlen(graphName) == 0)
		graphName = WinName(0,1)
	endif
	
	String traces = TraceNameList(graphName, ";", 1)
	Variable ntraces = ItemsInList(traces)
	Variable i
	String trace0 = StringFromList(0, traces)
	Wave w0 = TraceNameToWaveRef(graphName, trace0)
	Variable commonValue = w0[overlayPoint]
	
	for (i = 1; i < ntraces; i += 1)
		String tname = StringFromList(i, traces)
		Wave wn = TraceNameToWaveRef(graphName, tname)
		Variable YatOverlay = wn[overlayPoint]
		Variable dif = commonValue - YatOverlay
		ModifyGraph offset($tname)={0, dif}
	endfor
end