...

kalibrierschein/kalibrierschein.cls

@@ -153,12 +153,11 @@ footskip=0bp,
   BoldFont=*-bold,
   ItalicFont=*-italic,
   BoldItalicFont=*-bolditalic.otf] 
-\def\fira@weight{Regular}% wegen bug in "firamath-otf" (2018/09/17 v. 0.01)
-\RequirePackage[usefilenames]{firamath-otf}
+\RequirePackage[usefilenames,weight=Regular]{firamath-otf}
 \RequirePackage[italic]{mathastext}
- 
-\def\prim@s{\/\prime\futurelet\@let@token\pr@m@s}
 
+% Abstandskorrektur; Bug-Report an Autor von "mathastext"?  
+\def\prim@s{\/\prime\futurelet\@let@token\pr@m@s}
 \AtBeginDocument{\let\PRIME\prime
   \def\prime{\mkern2mu\PRIME}%
 }