Two hydrometers have different PA at the same SG?

[Grape Expectations]

Stevenson Reeves S1011 hydrometer: 1.100 SG = 15.9% PA (and 1.050 SG = 8.1% PA).
Stevenson Reeves S1310 hydrometer: 1.100 SG = 13.5% PA (and 1.050 SG = 6.6% PA).

Both made by the same company, both "suitable for both wine and beer".

Can anyone explain why the scales differ like this?

Both are manufactured calibrated the same, to 1.000 SG in water at 20°C.

I might end up not adding enough sugar to achieve the desired ABV when using the S1011 hydrometer, or conversely, I might add too much sugar and end up with a higher ABV than desired, if using the S1310 hydrometer. One has to be wrong, or both!

Personally, I'm just aiming at the max ABV I can produce and the 1st hydrometer I bought (S1011) only goes up to 17% PA. The 2nd one (S1310) goes up to 23% PA.

If this question has come up before then I apologise!

Cheers.

 

[BernardSmith]

Interesting question. The rule of thumb is to use 131.25 as the multiplier after you subtract final gravity from initial and my own rule of thumb is to simply use 131 as my multiplier - so a starting gravity of 1.100 = 13% ABV and a gravity of 1.050 cider , for example) = 6.5% ABV , which is the lower set.
The top line is using a multiplier of close to 160. Personally, I have never heard of that. Sounds nonsense to me BUT that said, I went to Amazon UK and read the reviews there and while one or two people said that theirs was badly calibrated, no one mentioned the rather strange potential ABVs you discuss.

 

[Rocky]

Stevenson Reeves S1011 hydrometer: 1.100 SG = 15.9% PA (and 1.050 SG = 8.1% PA).
Stevenson Reeves S1310 hydrometer: 1.100 SG = 13.5% PA (and 1.050 SG = 6.6% PA).

Maybe one is metric. (Sorry, could not resist that one)

 

[Grape Expectations]

I have been asking Chat GPT and it doesn't know either.

Since hydrometer S1011 predicts a higher PA at 1.100 SG, then it would have me not adding as much sugar as the S1310 would have me adding, to get the same ABV. I'll just play it safe and use the one that tells me to add more sugar, because I am aiming at a higher ABV rather than lower.

 

[BernardSmith]

Maybe one is metric. (Sorry, could not resist that one)

Where are percentages non metric?

 

[sour_grapes]

Just ignore the PA markings. They are notoriously "suspect," as you learned. Use Bernard's rule of thumb or use an online conversion calculator. I favor Fermcalc: FermCalc