FYI, I spent fifty years as an instrument engineer (I have a PhD Chem, but was designing measurement systems in grad school and never stopped). ALL quantitative science involves MEASUREMENT (including engineering). And the paper I posted a link to is all about measurement. No "theory" anywhere.
I suggest you actually read it.
You’re missing my point. Is the efficacy of the homemade t-shirt mask measured after being worn a few days without washing, being adjusted constantly with contaminated hands? If not, it’s meaningless.