Answer by James K. ·
For server side purepaths the response time is measured based on how long it takes for the first node in that purepath to complete and the time doesn't start until the request has actually reached that entry point. I believe that using something like the Chrome developer tools that are actually on the end user machine also includes the time that it takes the request to actually reach that entry point (i.e the front end web server).
By calculating the difference between your response times it looks like it is about between 140 and 150 so this might be the contribution to response time coming from the external network. If the response time from Dynatrace was higher than the Chrome measurement then that might be a more serious issue.