If you’re trying to use the Charts module to create cumulative graphs over time (in my case, race registrations). No time now for a detailed post.
This guy had the answer: http://drupal.stackexchange.com/questions/50066/how-to-add-up-rows-in-a-view
He cites this but I didn’t use it: https://www.drupal.org/node/1516348
This is the module you need, can only add field if you are User 1: https://www.drupal.org/project/views_php
My setup (I was pulling the order_id field and aggregating the results as a count):