Warning: rant about style ahead

$c=$w%24; if($c==0){$c=24;} $r=ceil($w/24); $n=(($c-1)*16)+$r;

Maybe if you used _words_ for variable names, more people would understand your code. I didn't even try to figure out what $c, $w, $r and $n are. This is for all programming, but for prototyping it is very, very important if you want to survive. Not everything is a 4-line script.

Whitespace also helps a lot:

$c=$w%24;              $c = $w % 24;
if($c==0){$c=24;}      $c ||= 24;
$r=ceil($w/24);        $r = ceil($w / 24);
$n=(($c-1)*16)+$r;     $n = (($c - 1) * 16) + $r;
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The second example is easier to read, imho. Note that I used ||=.

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