leak down test proceedurs

[HotRodShovel]

I've been doing some research on leak down testing.  At this point all I have affirmed is that the motor needs to have the front cylinder at TDC on the compression stroke.  After that I'm a bit confused on the test. So I pretty much know as close to nothing as you can get.
Should the motor be at operating temp or cold? 
How is the percentage determined? 
If any of the Guru's out there can give me a blow by blow of the test procedures and what to look for I'd be grateful.
Also what size gauge is the best for this purpose. I know there are many available.

As always...thanks in advance

[DresserDan]

I bought a leak down tester.It has all the instructions there.You have a steady air supply of a certain lbs of air and go from there.The tester will tell you all the %%% and details on how to tell what is leaking.

[HotRodShovel]

Thanks a lot.  I appreciate the help