Did you look at Settings.php line 144
$SITE['uomTemp'] = '°F'; // ='°C', ='°F'
$SITE['uomBaro'] = ' inHg'; // =' hPa', =' mb', =' inHg'
$SITE['uomWind'] = ' mph'; // =' km/h', =' kts', =' m/s', =' mph'
$SITE['uomRain'] = ' in'; // =' mm', =' in'
$SITE['uomSnow'] = ' in'; // =' cm', =' in'
$SITE['uomDistance'] = ' miles'; // or ' km' -- used for Wind Run display
$SITE['uomPerHour'] = '/hr';
//