English: An FTIR interferogram. The horizontal axis is the position of the moving mirror in the FTIR, the vertical axis is the amount of light measured by the detector. DETAILS: This was a "background" measurement, using a commercial FTIR. To make the fringes visible, I zoomed in the interferogram both vertically (the ZPD peak goes much higher and lower than shown) and horizontally. The mirror displacement units were not given, so I inferred it from the resolution quoted by the software. The vertical axis is arbitrary units -- unknown scale AND unknown offset!