Unit conversions and symbolic mathematics with Babel

[dieter@duenenhof-wilhelm.de (H. Dieter Wilhelm)]

Hello Org,

for some engineering most often I need estimations with unit
conversions, Emacs Calc is perfect for this.

When it comes to reporting and documentation I'd like to do it with
org-mode, of course.  For numerical stuff and visualisation purposes I'm
using already R and TikZ. But for unit conversions and symbolic maths
I'm in a bind when trying to do this with free programs.

- R :: Do you have experience with a units packages under the R-project?
  What I've seen so far is not so reassuring...

- Maxima :: I think there is a nice and intuitive units package for
  maxima.  But this would mean learning an additional tool and mentally
  switching between both within one document.

- Calc :: I'd prefer to do it with Calc but the Babel interface is
  (yet?) restricted

  For example, I can define functions and do some unit conversions:

    #+BEGIN_SRC emacs-lisp
    (defmath cvun(a b)
	  (math-convert-units a b))
    #+END_SRC

    #+RESULTS:
    : calcFunc-cvun

    #+BEGIN_SRC calc :var L1 = "5 mm" 
    cvun( L1, m)
    #+END_SRC    

    #+RESULTS:
    : 5e-3 m

  But what is missing is to assign variables within a source block
  
    #+BEGIN_SRC calc :var L1 = "5 mm" 
    L2 := cvun( L1, m)
    #+END_SRC    
  
  Unfortunately this is not working.  Do you have an idea how to
  implement this?

- Are you using (better) alternatives?

Thanks for your insights

       Dieter
-- 
Best wishes
H. Dieter Wilhelm
Darmstadt, Germany