IMHO newbie gains are much like the first gains that a deeply de-conditioned make when they first hit the gym— sort of a return to baseline norms.
As to measuring, I’ve said here before is that using a ruler or tape can encourage a false measurement by striving for more.
Instead I suggest going to your local Home Depot/ Lowe’s/ paint store and pick up a batch of paint stirrers to use as tally sticks— apply them the same as you would a ruler and mark off the measurement— then check the outcome with a hard ruler.
That way there is no ‘placebo’ effect
Plus you just date the fucker and store it for a visual collection of your PE gains. I also mark my girth gains on the back just for gits and shiggles.