The <b><a href="https://en.wikipedia.org/wiki/Minirex" class="extiw" title="en:Minirex">Minirex 75</a></b> with opened case, a calculator of the Minirex series started in 1973, manufactured in the GDR (East Germany) by the VEB Röhrenwerk Mühlhausen. This company was renamed into <a href="https://en.wikipedia.org/wiki/Kombinat_Mikroelektronik_Erfurt" class="extiw" title="en:Kombinat Mikroelektronik Erfurt">VEB Mikroelektronik</a> "Wilhelm Pieck" Mühlhausen.
Hans Wollny
Attribution
The author sent the photo to me.