Converting distance travelled and time taken into a speed

PHP Revision example from a Well House Consultants training course
More on PHP Revision [link]

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This example references the following resources:
http://www.wellho.net/course/php.html
http://en.wikipedia.org/wiki/Preferred_walking_speed
http://www.scientificamerican.com/article.cfm?id=walking-speed-survival

Source code: speed.php Module: H300


<?php

# Converting distance travelled and time taken into a speed

# If all data is complete, calculate result

if ($_REQUEST[t_units] > 0 and $_REQUEST[d_units] > 0 and
        $_REQUEST[time] > 0 and $_REQUEST[distance] > 0) {

        $d = $_REQUEST[distance] * $_REQUEST[d_units];
        $t = $_REQUEST[time] * $_REQUEST[t_units];

        $mph = $d / $t / 63360 * 3600;
        $kph = $d / $t / 39370 * 3600;

        $report = sprintf("%d inches in %s seconds - that's %.2f mph or %.2f kph",
                        $d, $t, $mph, $kph);

} else {

# If we are short of data, is it because we have just arrived at the page  ...

        if ($_REQUEST[t_units] == "") {
                $report = "Result will appear here";

#  ... or because the form hasn't been fully and properly completed?

        } else {
                $report = "I need you to enter a positive value in each box and select both unit types";
        }
}
?>
<html>
<head>
<title>Speed Conversion - timed movement to mph and kph</title>
</head>
<body>
<h3>Convert an observation into a normalised speed</h3>
<?= $report ?>
<hr>
<h3>Please tell me how long and how far</h3>
<form>

Time taken <input name=time>
<select name=t_units>
<option value=0>Please select:</option>
<option value=1>Seconds</option>
<option value=60>Minutes</option>
<option value=3600>Hours</option></select><br />

Distance covered <input name=distance>
<select name=d_units>
<option value=0>Please select:</option>
<option value=1>inches</option>
<option value=12>feet</option>
<option value=36>yards</option>
<option value=63360>miles</option>
<option value=0.3937>cms</option>
<option value=39.37>metres</option>
<option value=39370>kilometres</option></select></br>

<input type=submit></form>

<hr>
<i>This is a PHP example program - a single page with a number of facilities shown, for use early on during
a </i><a href=http://www.wellho.net/course/php.html>PHP course</a><i>.  In writing it, we have tried to
ensure that there are no security holes exposed by the page,
but we have not gone into full error handling, data echo back, sticky fields, etc to turn it into a really
nice application, nor have we given the page a pretty look and feel.</i><br><br>
For comparative purposes when you look at the results, the average person walks at around 3 m.p.h - see
<a href=http://en.wikipedia.org/wiki/Preferred_walking_speed>[here]</a>. Older people - the over 65s -
average around 2.8 m.p.h. - see <a href=http://www.scientificamerican.com/article.cfm?id=walking-speed-survival>[here]</a>.
</body>
</html>

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* PHP Techniques
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