gistfile1.php

<?php 
/* 
    This creates a global variable called SG_STATIC with the full absolute URL to the static directory.
    Note: this will only work if you're creating the statement inside of the base directory of your plugin
*/
define('SG_STATIC', WP_PLUGIN_URL.'/'.basename(dirname(__FILE__)).'/static');

// For example:
echo SG_STATIC;

// Will print out http://wordpress_server.com/wp-content/plugins/plugin_folder_name/static

// So in your situation, you could easily do something like
define('MYPLUGINNAME_DIRECTORY', WP_PLUGIN_URL.'/'.basename(dirname(__FILE__)));

// And then in your use you can do the following
echo '<img src="'.MYPLUGINNAME_DIRECTORY.'/runners-log-chart.png" alt="image" />';

/*
    Which will print out: 
    <img src="http://wordpress_server.com/wp-content/plugins/runner_plugin_folder/runners-log-chart.png" alt="image" />
*/

?>