It’s not uncommon to hear about “relative” and “absolute” measurements when talking about laser power measurements. Those are simply two different ways to approach and define the meaning of your readings. So, let’s sort this out.
Absolute Power Measurement
First, an absolute power measurement needs to come down to the basics of the known physics, so what actually is a watt? Once this question is answered, then, by a very rigorous process, you can determine what the actual value of a watt should be according to its definition. That being said, you still have to understand that even with a very strict protocol, the “True value’’ is always known only within a certain uncertainty.