if you are using "relative" in a geological term, then perhaps yes. I have read documents dating back 50 years using this technique.
I first put my hands on software for this in 1988 - then using an HP300 series computer with an IEEE interface to a spectrum analyser.
The hardware took a leap forward about 4 years later and the only real changes since then seem to be just at the edges.
It is an extremely useful tool and I have helped baffled engineers solve many problems with it.