How is total HTML size and script size calculated?

In Damian Edwards' video What’s new in ASP.NET Web Forms 4.5:

http://channel9.msdn.com/Events/Visual-Studio/Visual-Studio-2012-Virtual-Launch/What-s-new-in-ASP-NET-Web-Forms-4-5

he shows an example of Unbobtrusive Validation in ASP.NET 4.5. In the example he has a page which shows the total HTML page size and how much is script.

How are these two values calculated?