Displaying the Diff of Entries

Anon

Hi Everyone,
I am trying to display the difference between entries. I would like to view a column next to display the mileage diff from 2002-08-01 & 2002-07-01. Basically on july 1 my mileage was 535 and on aug 1 my mileage is 631, how many miles did I put on the vehicle? This will a continous display like below.

Date Mileage Difference
2002-08-01 631 96
2002-07-01 535 135
2002-06-01 400

Thanks for any help
:o) Ivan

My code looks like this so far:

$sql = "
SELECT *
FROM mileage, lsv
WHERE mileage.vid = \"$vid\"
AND mileage.vid = lsv.vid
ORDER BY mileage.stop DESC
";

$result = @($sql,$connection) or die("Couldn't execute query.");

$the_mileage = "

<tr>

<td bgcolor=#800000 width=125>Stop Mileage:</td>

<td bgcolor=#800000 width=125>Total From Last Entry:</td>

</tr>

while ($row = mysql_fetch_array($result)) {

$id = $row['id'];

$vid = $row['vid'];

$stopdate = $row['stopdate'];

$stop = $row['stop'];

$howmany = $row['howmany'];

$reg = $row['reg'];

$sn = $row['sn'];

$org = $row['org'];

$vco_n = $row['vco_n'];

$vco_e = $row['vco_e'];

$the_mileage .= "<tr>

<td bgcolor=#ECDC94 width=125>$stopdate</td>

<td bgcolor=#ECDC94 width=125>$thediff</td>

Anon

Easy enough. Have a variable $previous_mileage. Set it to 0 before the loop and just before the end of the loop set it to $the_mileage.

Then the monthly difference is $the_mileage-$previous_mileage.

Anon

OK. Let's see if I understand this correctly. Before the loop I created a variable.

$previous = 0;

Now, this is where I am lost. Before the end of the loop I have:

$mileage - $previous

This displays something like 535 - 0.

Where did I go wrong???

:o) Ivan