You can measure how efficient a PCR is by how long it takes to get a positive result. PCR requires a loop of different temperatures to cause different steps in

You can measure how efficient a PCR is by how long it takes to get a positive result. PCR requires a loop of different temperatures to cause different steps in the reaction to occur. This loop is usually repeated 30-40 times. You measure if its positive by looking for a (continuous) light signal. The light signal increases each time you loop through the temperatures. When the light signal passes a pre-determined threshold, that cycle is said to be the one where you got the positive result. The more virus DNA/RNA in the sample, the less loops you need for a positive result.