[the OlLine Rebel]

What the heck is PCR?

I wish people would follow standard old-fashioned English writing guidelines.

[goodnesswins]

From WebMD
What is a PCR test?
ANSWER

A PCR test stands for polymerase chain reaction test. This is a diagnostic test that determines if you are infected by analyzing a sample to see if it contains genetic material from the virus

[Svartalfiar]

What the heck is PCR?

I wish people would follow standard old-fashioned English writing guidelines.

Polymerase-Chain Reaction. It's basically a testing method that takes whatever is in your system and multiplies it until it's detectable. It works by finding DNA fragments, splitting them, then rebuilding them. Repeat. Repeat. etc. 20 or so cycles is the normal process, which means 2^20, or just over 1MMx as many particles are present. However, the ChinaVirus tests are doing 40+ cycles, which is 1T times as many as the original. If any tiny piece of the virus was originally present, it's almost certain to be detected.

This test is very useful when you have symptoms but an unknown cause, as it can easily tell which viri/bactria you have in your system.
It is useless for determining if an asymptomatic person has an active infection, as it takes months for your body to completely remove all remaining viral fragments from your system. Also, the test only looks at DNA - so it doesn't depend on having live, active virus particles in you, which is what would actually cause infection/infectivity.