Before I get too tired (it's 3:25 here) I have an idea which might be interesting for the OP.
IF your process is clearly repeatable, you could:
a) Make 10 samples of 10 different degrees of alcohol reduction;
b) Make accurate measuring of whatever parameter you find differentiating enough: refraction index with a refractometer, gravity with a hydrometer in the proper density range, or anything else like weight (with one of those scales that go to the 1000th of gram and that actually work), colour, whatever you have an instrument for.
c) Give those 10 samples to a laboratory for a serious and precise alcohol content response using the most precise method they can;
d) Make a table of the 10 ABV values the laboratory gave you and the 10 values that you observed at home.
If they make a nice curve, or even better a nice line on a graph, then you don't need to send any more sample to the lab.
For each beer you make, you can measure your own value and relate it to the table.
The problem here is "repeatability" of course. You could postpone this until you have a recipe that you can brew with good uniformity, and a measuring method that you have nailed down with sufficient accuracy.
If a hydrometer or a refractometer differentiate enough your samples at different ABV, you can pay the lab only once.
IF your process is clearly repeatable, you could:
a) Make 10 samples of 10 different degrees of alcohol reduction;
b) Make accurate measuring of whatever parameter you find differentiating enough: refraction index with a refractometer, gravity with a hydrometer in the proper density range, or anything else like weight (with one of those scales that go to the 1000th of gram and that actually work), colour, whatever you have an instrument for.
c) Give those 10 samples to a laboratory for a serious and precise alcohol content response using the most precise method they can;
d) Make a table of the 10 ABV values the laboratory gave you and the 10 values that you observed at home.
If they make a nice curve, or even better a nice line on a graph, then you don't need to send any more sample to the lab.
For each beer you make, you can measure your own value and relate it to the table.
The problem here is "repeatability" of course. You could postpone this until you have a recipe that you can brew with good uniformity, and a measuring method that you have nailed down with sufficient accuracy.
If a hydrometer or a refractometer differentiate enough your samples at different ABV, you can pay the lab only once.