Hi Colomet,
We get the used memory with the PHP function memory_get_peak_usage(). More info: https://php.net/manual/en/function.memory-get-peak-usage.php (PHP 5 >= 5.2.0, PHP 7).
This value should reflect the memory used by WordPress. The plugin uses a standard PHP function memory_get_peak_usage() and we can’t influence the value.
We have checked the UsageDD plugin and it uses the same function to get the used memory by PHP:
$memory_usage = round(memory_get_peak_usage() / 1048576, 2);
We have checked on some of our installations and the displayed memory usage of both plugins are quite similar.
The difference on your installation can be because the two plugins don’t execute at the same moment. Each plugin displays the peak amount of memory at the moment it executes. That’s the only explanation we find.
Unfortunately we get the data from a standard PHP function and can’t investigate further.
Best regards from Spain.
