Need help with variables/includes

I have two php pages, the first of which has a "config section"

In the config section of the first page, I would like to have the ability to designate a variable f or c, which would change the $units='f', which is in a function on the second page here:

function getWeather($zip, $units='f') {

Help! :)

Just set the variable(say $default_unit):
$default_unit = 'f';
and change the function call to:
getWeather($zip, $default_unit);