The Hard Vacuum Inside/Out technique is one of the most common, and most effective forms of leak detection.  Inside/Out refers to the direction of flow the Helium takes as the test part leaks.  In the case of Inside/Out testing, the test part is pressurized with Helium, with a vacuum drawn around the part inside the vacuum chamber.  The mass spec measures the amount of helium that flows/leaks from inside the test part out to the vacuum chamber.  

This method offers measurable leak rates as low as 10^-9 std. cc/sec, and as high as 10^-3 in high volume production applications.  This technique features high sensitivity, flexibility, and temperature and test time independency. 

Disadvantages include:  a higher cost than the Effect of the Leak testing methods, requires consumables, vacuum pump down time dependent, rough vacuum requires more highly skilled maintenance,  test parts must be clean and dry, vacuum pump oil waste, and the location of the leak is not identified.

The test typically consists of the following steps:

	Evacuating the chamber to a low enough vacuum
	Pressurizing the part with Helium
	Monitoring Helium levels inside the chamber

Sensitivity range [std.cc/sec]
Temperature dependence
Operator dependence
Main factors affecting accuracy	Chamber volume Test time
Test pressure range	any
Maintenance required	Qualified maintenance required for vacuum pumps and Mass Spec.
Cost