A simple "StopWatch" class to measure PHP execution time. The class can handle multiple separate timers at the same time.

StopWatch.php

<?php
class StopWatch {
  /**
   * @var $start float The start time of the StopWatch
   */
  private static $startTimes = array();

  /**
   * Start the timer
   * 
   * @param $timerName string The name of the timer
   * @return void
   */
  public static function start($timerName = 'default'){
    self::$startTimes[$timerName] = microtime(true);
  }

  /**
   * Get the elapsed time in seconds
   * 
   * @param $timerName string The name of the timer to start
   * @return float The elapsed time since start() was called
   */
  public static function elapsed($timerName = 'default'){
    return microtime(true) - self::$startTimes[$timerName];
  }
}

Usage: