I may still not understand exactly what you're trying to do. But if you want to keep track of a max value for each time/database at the same time that you're keeping a total for the purpose of averaging, you could do something like this inside your while() loop:

$h{$ddhh  }{$database}{total} += $speed;
$m{$ddhhmm}{$database}{total} += $speed;
$h{$ddhh  }{$database}{max}    = max(($h{$ddmm}{$database}{max} || 0),
+ $speed);
$m{$ddhhmm}{$database}{max}    = max(($h{$ddmm}{$database}{max} || 0),
+ $speed);
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You can use the max() function from List::Util or write your own. Now later in the code where you used to access the total speed with $h{$timestamp}{$database}, you'll change that to access it as $h{$timestamp}{$database}{total}. And that makes room to keep track of the maximum value for each one in $h{$timestamp}{$database}{max}. Make sense?