Why do these hydrometer scales differ? Stevenson Reeves "S1011/U" vs "S1310"

[Grape Expectations]

EDIT: I already posted about this a year back, but without the chart, sorry!
https://www.winemakingtalk.com/threads/two-hydrometers-have-different-pa-at-the-same-sg.77396/

I have two Stevenson Reeves hydrometers: The S1011/U with a range of 5% PA to 17% PA and coloured bands, then the S1310 with a range of 0% PA to 23% PA that's plain old black and white.

I noticed a while back, they don't match up when I look at the PA and SG levels on them, so I made a chart.

The S1011/U (in red) shows a lower SG level for any given PA level, compared to the S1310 (in blue).

Does anyone know if there's a reason for this? The one I use is the S1310. If I aim at 1.100 SG with that, it lines up with 13.5% PA on the scale. If I use the other hydrometer, then 1.100 SG lines up with almost 16% PA - quite a big difference isn't it!

Which one is closest to reality?

Are they both wrong, or is at least one of them right?

 

[Raptor99]

PA is only an estimate based on SG, which itself is only an approximation of the actual sugar content. There are a number of different formulas to estimate PA from initial SG. Go to FermCalc at https://fermcalc.com/FermCalcJS.html. Click on the Alcohol calculator. There are 9 different methods of calculating PA from SG, with a variety of different answers. For 1.100 OG, the ABV estimates range from 12.5 to 14.3%. So I suspect that the hydrometer reading 16% ABV is way off.

It is good to remember that PA is only an estimate. If you want the details on the methods, you can find them here: https://fermcalc.com/potential-alcohol/

 

[Christopher Anderson]

EDIT: I already posted about this a year back, but without the chart, sorry!
https://www.winemakingtalk.com/threads/two-hydrometers-have-different-pa-at-the-same-sg.77396/

I have two Stevenson Reeves hydrometers: The S1011/U with a range of 5% PA to 17% PA and coloured bands, then the S1310 with a range of 0% PA to 23% PA that's plain old black and white.

I noticed a while back, they don't match up when I look at the PA and SG levels on them, so I made a chart.

The S1011/U (in red) shows a lower SG level for any given PA level, compared to the S1310 (in blue).

Does anyone know if there's a reason for this? The one I use is the S1310. If I aim at 1.100 SG with that, it lines up with 13.5% PA on the scale. If I use the other hydrometer, then 1.100 SG lines up with almost 16% PA - quite a big difference isn't it!

Which one is closest to reality?

Are they both wrong, or is at least one of them right?

View attachment 114140

I have 4 hydrometers. All read differently. The reasons? the chart inside is mispositioned during assembly. they are calibrated wrongly, BUT IT DOESN'T MATTER. I have tested all of them and though the initial SG is all different (and the end SG also), they all show that they are working. Pick one to use and use it!! It is like having two watches/clocks. They could be seconds off but still be accurate. IMHO