We've got a customer comparing campaigns tracked with both Return Path and Litmus analytics. I know that trying to "unify" different analytics systems is a virtually impossible. But, I'd like to know what Return Path considers a "read." Litmus is crystal clear about how its analytics break down - skim vs. read are based on time spent viewing the email. In Return Path, is a "read" purely that the tracking pixel was triggered due to email being opened by recipient with images enabled, or is it more involved? Thanks!