We recently discovered that the PTM software is no longer available from the HPLabs website.  We have placed both the Mac and Windows versions of the PTMFitter in a dropbox along with the license file from HP.  You can get the software from here: https://www.dropbox.com/sh/jfsy0lhxu6zv4i4/AADJpq6E_GJmNw_s5C8r94CVa?dl=0 Also - many papers on PTM and RTI are by Tom Malzbender - and you can find them on his personal website: https://sites.google.com/site/tommalzbender/