What the heck?
If would use <A href='@url@'>blablabla</A> you would get this url:
<A href='calculate-resistance?volt=2&amp=2<blablabla>/A>
This is of course plain nonsense...
However, if you use the correct <A href='@url;noquote@'>blablabla</A> you get:
<A href='calculate-resistance?volt=2&=2'>blablabla</A>
... which is the correct way to pass the variables volt and amp to the url.
Quoting is allways wrong within links. URL-encoding is ok. I.e. if you want to pass a variable containing &, you would URL-encode it.