SRM400 with Arduino Nano

Hi,
I am relatively new to Arduino, so far I've only managed to modify previous peoples code for things like bluetooth and temperature sensing but have written a few simple programs in C for pic at uni

I have bought an SRM400 from rapidonline: Prowave SRM400 Sonar ranging module | Rapid Online
Datasheet: http://www.rapidonline.com/pdf/35-1830.pdf

I've wired it up as per the diagram in the datasheet and plan to use it for reading a distance measurement but I am a bit stuck for how to read an output. i.e. which function would be most appropriate.

If anyone has used the SRM400 before or understands how best to interface with it, your knowledge and assistance would be most appreciated as I have not been able to find anyone else who has used it online.

Thanks in advance
Luke