Read Analog Current Input

Hi

Firstly , i want to read analog current up to 20 mA then i want to convert this value to distance unit[mm].

First question:

How can i read analog current input ?(which sample code sholud i use for this job)

i have input cable which contains +,- terminal.i think that "+" is related to analog current input ,"-" is 0V/ground connection.

second question:

which terminal/pin should these two cable be connected on arduino board ?

That is a normal standard 4-20mA output of a sensor ? Use a schematic like the one that is attached to this : http://forum.arduino.cc/index.php?topic=188067.msg1391860#msg1391860

Or do you really want to measure a current of 20mA ? Like the current through a led ?

thank you

i will try this way :)