Fuel consumption

<?php
    /*
    Copyright (c) 2009, reusablecode.blogspot.com; some rights reserved.
    
    This work is licensed under the Creative Commons Attribution License. To view
    a copy of this license, visit http://creativecommons.org/licenses/by/3.0/ or
    send a letter to Creative Commons, 559 Nathan Abbott Way, Stanford, California
    94305, USA.
    */
 
    /*
    NOTE: The "magic numbers" in these functions are from the 2007 Fuel Consumption Guide
          published by Natural Resources Canada and use a conversion of 4.546 L = 1 imperial gallon.
          U.S. fuel economy ratings use U.S. gallons which are 20% smaller than imperial gallons.
    */
 
    // Calculate fuel consumption rating in litres per 100 kilometres
    function lph($kilometres, $litres)
    {
        return ($litres * 100) / $kilometres;
    }
 
    // Calculate fuel consumption rating in miles per gallon.
    function mpg($miles, $gallons)
    {
        return $miles / $gallons;
    }
 
    // Convert miles per (imperial) gallon to litres per 100 kilometres.
    function lph2mpg($mpg)
    {
        return 282.48 / $mpg;
    }
 
    // Convert litres per 100 kilometres to miles per (imperial) gallon.
    function mpg2lph($lph)
    {
        return 282.48 / $lph;
    }
 
    // Calculate fuel consumption in litres.
    /*
    distanceTravelled = the distance travelled in kilometres; e.g. 20000
    percentCity = the percentage of the distance travelled occuring in the city; e.g. 0.55
    percentHighway = the percentage of the distance travelled occuring on the highway; e.g. 0.45
    ratingCity = city fuel consumption rating in litres per 100 kilometres; e.g. 7.9
    ratingHighway = highway fuel consumption rating in litres per 100 kilometres; e.g. 5.9
    */
    function fuelConsumption($distanceTravelled, $percentCity, $percentHighway, $ratingCity, $ratingHighway)
    {
        $cityConsumption = ($distanceTravelled * $percentCity * $ratingCity) / 100;
        $highwayConsumption = ($distanceTravelled * $percentHighway * $ratingHighway) / 100;
        $fuelConsumption = $cityConsumption + $highwayConsumption;
    }
 
    // Calculate carbon dioxide emissions in kilograms.
    function CO2emissions($fuelConsumption, $fuelType)
    {
        return $fuelConsumption * (($fuelType == 'diesel') ? 2.7 : 2.4);
    }
?>