phpWX - What Variable To Pass?

Hello,

I downloaded this cool PHP for displaying the weather...

Problem is, the developer does not provide very much help in setup.

If i add a line that reads:

$zip_code = '20166'

to the top of the code (under comments), then browse to it, it works... if i take that line out, it says i did not provide a good zipcode.

I need to know the format of the URL with it's variables so i can just use link code like this:

<a href=http://mydomain.com/weather/index.php?whatever=20164>Check 20164</a>

You can get info on the thing here:

Help!

Thanks!

Beavis2084