To quote from a brief article by Angus Gorlay:
"The NHS is using 45 (yes, FORTY FIVE) cycle amplifications (or iterations) in the PCR test. That means they double the magnification of the sample 45 times (double it, then double that, then double that, then double that etc etc. Comes out at 16 trillion I think)
To try to further clarify the issue with the PCR let's explain further.
The PCR test will detect in a sample, minute remnants of the DNA material from past infections with one of the coronaviruses.
So imagine Joe had one of the viruses known as "flu" back in, say 2018. The virus has dong since died but it has left in his body tiny harmless fragments of its DNA. It is these fragments that the PCR test will detect if they are there and if it detects some, it registers a "positive."
If he registers positive then government will call him a "COVID Case".
For a person to be declared to be a COVID case that is all that has to happen. But the PCR test detects remnants of the DNA of past infections. It does NOT mean that the person has a "live" infectious virus in his body.
But how tiny can these traces be? Well, here is what has to be done for them to be "seen":
The sample being tested will be magnified until tiny amounts show up.
The more minute the traces of DNS fragments, the more the sample has to be amplified (Think of it the way a magnifying glass or microscope magnifies what you are looking at) in order to "see" them.
This amplification is called "cycles." So if sample had undergone, say, 3 cycles it has been doubled, then doubled, then doubled.
Tom gets his shirt back from the cleaners. He asserts there is speck of dirt on the collar.
Nobody can see the speck as it is too small so to "prove" there is a spot of dirt on the collar, he puts the collar under a microscope and magnifies it by two.
But still the speck of dirt is too small to be seen.
So he magnifies it by two again so that it is now four times its normal size.
Still no dirt is visible because the spot is as yet too small to be seen.
So he doubles it again, a further "cycle" of amplification that now makes the collar appear eight times its normal size.
Still no speck of dot is visible so does another cycle and magnifies it by two so that it is now 16 times it original size.
Still no dirt.The collar has been through three cycles of amplification but the speck of dirt remains too small to be seen.
And so on.
He keeps doubling, then doubling,then doubling, then doubling up to, say 45 times.
By my math that takes us to somewhere around 42 thousand billion times the actual size of the sample.
A spot that takes that muh amplification has to be pretty damn tiny.
To give you an idea, imagine the spec of dirt on the collar was a thousandth of a millimetre in size. too small to be seen with the naked eye. Magnify that one-thousandth-of-a-millimetre spot by 1.5 billion times and you have something that is about a of a million kilometres across.
That's quite a lot of magnification and you'd have to be pretty determined to find a speck of dirt to go to thosoe lengths.
So you say, triumphantly.
"There see! The collar is dirty"!