.ibw file, multidimensional wave, auxiliary x and y points

What you see in the topmost 'row' (actually not a real row but a 'label' of each column) is most probably the y-scaling of your data. You can change the wave's scaling either directly via the data browser or from the menu by going to 'Data => Change Wave Scaling ...'. To read more about scaling execute the following in the command line:

Yes, that row shows the Y scaling of your wave. To learn more, execute DisplayHelpTopic "The Waveform Model of Data" and DisplayHelpTopic "Multidimensional Waves".

To get a Y value (yes, we call it Y even though it is the horizontal dimension in a table) you can do this:

print IndexToScale(Device_0000, colnum, 1)

Replace "colnum" with the actual column number of your wave.

To be precise, it is a "Y index value", analogous to the "X index values" displayed vertically.