add_filter( 'woocommerce_product_tabs', 'custom_tab' );
function custom_tab( $tabs ) {	
	// Adds the new tab
	$tabs['test_tab'] = array(
		'title' 	=> __( 'Measurement charts', 'woocommerce' ),
		'priority' 	=> 50,
		'callback' 	=> 'custom_tab_content'
	);
	return $tabs;
}
function custom_tab_content() {

	// The new tab content

	echo '<h2>Measurement charts</h2>';
	echo '<p>Lorem ipsum dolor sit amet consectetur adipiscing elit ultricies convallis volutpat, placerat proin scelerisque eget velit tellus at nibh risus. </p>';
	
}