I need to code a float with magnitude (ie unit of measure)

I'm apologize about my poor english

I need to a "double precision" with magniude (ie meters, kilo, dolar, 
etc). And can operate with them (ie dolar+dolar=dolar or 
dolar/dolar=double precision).

Do you know some pluggin or module to do this?

I can implement it but I need some examples. I try the example of 
chapter "User-Defined Types" but I don't know how to compile in windows 
(with MinGW). I just try some thigns that breaks postgres.exe.

Can you send me an example (with c code and makefile to see how to 
compile). Simple example is ok. The Manual example is not enaugh 
complete for me.

Thanks

Emilio Platzer
PD ¿Do you like to send yo some of my experiments?