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> From: çağlar girit <cog@pelagi.cc>
> Date: Sun, 26 Jan 2025 22:42:25 +0100
> 
> Thanks for getting back to me.  I didn't omit anything.  Maybe 
> it's a problem with my setup.  I removed the elc files and started 
> an edebug and found that the error happens when trying to build 
> the units table (math-standard-units in calc-units.el) when it 
> encounters the entry:
>     ( dB      "(ln(10)/20) Np" "decibel"))
> 
> Instrumenting math-find-base-units-rec, I found that the following 
> clause executes when parsing the string "(ln(10)/20) Np"
> 
> 	  ((eq (car expr) 'var)
> 	   (or (eq (nth 1 expr) 'pi)
> 	       (error "Unknown name %s in defining expression for 
> 	       unit %s"
> 		      (nth 1 expr) (car math-fbu-entry))))
> 
> So for some reason it considers 'ln' as a variable, like 'pi'.  If 
> I replace '(ln(10)/20)' by its numerical value in the units table, 
> there is no error anymore.  I guess '(ln(10)/20)' is not being 
> correctly evaluated as an expression while parsing the units 
> table?

If you haven't omitted anything from the steps, then I don't
understand why I don't see the problem.  And since I don't see the
problem, I cannot correlate what you say above with the problem.

Here's what I see after performing the steps you describe in Emacs 31: