The precursor to the sliding design/single battery wm10 series was the obscure TCM-10 dictaphone ....The wm10/wm20 was and its radio models wmF10/F20 was later given a makeover and became the wm30/10II with corresponding radio models that included both AM & FM. The strangest modification was putting two back to back making it a double deck capable of recording from the other side the wm w800. For now a not so great pic of the Various Shades of Envy 
I didn't realize there were that many variations of the WM10. Thanks for the pic! I am working on getting my original WM-10 working again! 
