How to add ‘total’ value to custom column title on the posts list page

WebElaine, if you are asking about global variable, i am doing something like this:

global $total_len;

...
function len_columns_content($column_name, $post_ID) {
...
if ($length) {
    $total_len += $length;
    echo $length.' symbols'.'total: '.$total_len;
}
...

and in every string i have get $total_len equal $length, as if $total_len is not global