In order to try and nail whether my ‘too much yeast in sample’ theory on preciously misses final gravity targets was correct, I took samples at start, ~25%, ~50% and ~75% of the way through the transfer for refractometer measures and an additional hydrometer sample at ~75%.
Somewhat frustratingly the refractometer result was the same for all 4 samples and around the same high level of previous brews (around 1.042 specific gravity)..
.. however the hydrometer returnes 1.022 a mere 0.006 above my final target!
One of these devices requires tuning (by a clueless me) and the other is likely accurate!
So the estimated ABV on the brewsheet is 8.9% (though the brewer’s friend calculator corrects that to 8.8%) and I have hit 8.01%!
I shall celebrate in a few weeks once it has carbonated!
The refractometer requires manual tuning and it could be that I've not done that well, maybe the water when doing so was way too cold or something. So of the two, much less likely to be accurate.
It makes sense as my beer a few brews ago kicked like a mule, but according to my measurements merely breaches 4%.. I suspect that if I'd used the hydrometer it would have told a different story!
I calibrated it with water, but I suspect it was too cold. So I am pleased to see you mention temperature sensitivity!
Calculations? Just reading the specific gravity, then entering the Original and Final gravity figures into the Brewer's Friend website calculator. Still very much a novice in this respect.
I tuned it to the same measurement as the hydrometer with the correct temperature wort so will see if it is even close to the original gravity next time I brew!
When I last used one we had to check the calibration with purified water and a certified test piece at 20ºC +/- 0.5ºC before we could use it for analysis. The instrument had a built in temperature probe and had cooled/heated water pumped through it to maintain the temp.
Others I've used in the past didn't have the water to maintain the temp but we made sure that the sample was at the correct temp.
Occasionally some samples tested were done at 16ºC.
This is a link to an older edition of the European pharmacopoeia extract detailing the requirements
There's a bit about viscosity on the next page you may find interesting.
I've used all the techniques mentioned on those pages.