Custom performance profiler

/**
 * Very simple time & performance measurment
 *
 * 1. Hook first function to the first available action
 * 2. Hook second function to the last
 * 3. Calculate the differences
 *
 **/

class measureUsage {

    private $records;
    private $all_records;
    private $average = array(
          'runtime' => 0,
          'repeated_runtime' => 0,
          'memory'  => 0,
          'ticks'   => 0,
          'queries' => 0
    );
    private $runtime;
    private $memory;
    private $ticks;
    private $queries;
    private $key;

    function __construct($key = false, $reset = false) {
      if ($key === false || is_admin()) return false;
      $this->key = $key;
      if ($reset === true) {
        delete_option('measure_performance');
        return false;
      }
      declare(ticks=1);
      register_tick_function(array(&$this, 'ticks'), true);
      $this->all_records = get_option('measure_performance');
      $this->records = &$this->all_records[$key];
      $this->records = !isset($this->all_records[$key]) ? array() : $this->records;
      add_action( 'registered_taxonomy', array( $this, 'start_measuring') );
      add_action( 'shutdown', array( $this, 'stop_measuring') );
    }

    function start_measuring() {
      $this->runtime = microtime(true);
    }

    function stop_measuring() {
      $this->runtime = microtime(true) - $this->runtime;
      $this->memory = memory_get_usage(true);
      $this->queries = get_num_queries();
      $this->save();
      $this->print_results();
    }

    function ticks() {
       $curr = memory_get_peak_usage(true);
       $this->memory = $curr > $this->memory ? $curr : $this->memory;
       $this->ticks++;
    }

    function save() {
      if (count($this->records) >= 20)
        array_shift($this->records);
      $this->records[] = array(
        'runtime' => $this->runtime,
        'memory'  => $this->memory,
        'ticks'   => $this->ticks,
        'queries' => $this->queries
      );
      $this->count_averages();

      // Store the average to the core key and the records as well
      if ($this->key == 'core')
        $this->all_records['core_avg'] = $this->average;

      update_option('measure_performance', $this->all_records);

    }

    function count_averages() {
      $count = 0;
      foreach($this->records as $k=>$v) {
        $count++;
        $this->average['runtime'] += $v['runtime'];
        if ($count > 1)
          $this->average['repeated_runtime'] += $v['runtime'];
        $this->average['memory'] += $v['memory'];
        $this->average['ticks'] += $v['ticks'];
        $this->average['queries'] += $v['queries'];
      }
      $this->average['runtime'] = $this->average['runtime'] / $count;
      if ($count > 1)
        $this->average['repeated_runtime'] = $this->average['repeated_runtime'] / ($count-1);
      $this->average['memory'] = $this->average['memory'] / $count;
      $this->average['ticks'] = round($this->average['ticks'] / $count);
      $this->average['queries'] = round($this->average['queries'] / $count);
    }

    function print_results() {
       ?>
       <table class='gridtable'>
        <thead>
          <tr>
             <th colspan=5>Measures for <strong><?php echo $this->key; ?></strong></th>
          </tr>
        </thead>
        <thead>
          <tr>
             <th>Measure no.</th>
             <th>Load time</th>
             <th>Memory consumption</th>
             <th>PHP ticks</th>
             <th>Database Queries</th>
          </tr>
        </thead>
       <?php
       $count = 0;
       foreach ($this->records as $k=>$v) {
        $count++;
        extract($v);
        $avgs = $this->all_records['core_avg'];
        if ($this->key != 'core') {
          $runtime -= $avgs['runtime'];
          $memory -= $avgs['memory'];
          $ticks -= $avgs['ticks'];
          $queries -= $avgs['queries'];
        }
       ?>
       <tr>
        <td><?php echo $count; ?>.</td>
        <td><?php echo number_format($runtime, 3, '.', ''); ?>s</td>
        <td><?php echo $this->mem_convert($memory); ?></td>
        <td><?php echo $ticks; ?></td>
        <td><?php echo $queries; ?></td>
       </tr>
       <?php
       }
       extract($this->average);
        if ($this->key != 'core') {
          $runtime -= $avgs['runtime'];
          $memory -= $avgs['memory'];
          $ticks -= $avgs['ticks'];
          $queries -= $avgs['queries'];
        }
       ?>
       <tr>
        <td><strong>Averages</strong></td>
        <td><?php echo number_format($runtime, 3, '.', ''); ?>s</td>
        <td><?php echo $this->mem_convert($memory); ?></td>
        <td><?php echo $ticks; ?></td>
        <td><?php echo $queries; ?></td>
       </tr>
       <tr>
        <td><strong>Core Averages</strong></td>
        <td><?php echo number_format($avgs['runtime'], 3, '.', ''); ?>s</td>
        <td><?php echo $this->mem_convert($avgs['memory']); ?></td>
        <td><?php echo $avgs['ticks']; ?></td>
        <td><?php echo $avgs['queries']; ?></td>
       </tr>
       <?php if ($this->key != 'core'): ?>
       <tr>
        <td><strong>Average plugin load</strong></td>
        <td colspan=4><?php echo $runtime / $this->average['runtime'] * 100; ?>%</td>
       </tr>
       <tr>
        <td><strong>Average plugin load on repetitive pageload</strong></td>
        <td colspan=4><?php echo ($this->average['repeated_runtime'] - $avgs['runtime']) / $this->average['repeated_runtime'] * 100; ?>%</td>
       </tr>
       <?php endif ?>
       </table>

       <?php
    }

    function mem_convert($size) {
        $unit=array('b','kb','mb','gb','tb','pb');
        return @round($size/pow(1024,($i=floor(log($size,1024)))),2).' '.$unit[$i];
    }
}

$o = new measureUsage('bwsrp');