From the HBD Archive
From: polstra!jdp@hplabs.HP.COM (John D. Polstra)
Subject: Re: specific gravity measurement problem
Date: 1989-06-07 01:06:12 GMT

In Digest #166, Martha Garske explained how to adjust an S.G. reading
to account for more water that has been added:

> Since water has an S.G.
> of 1.000 ( it is, in fact, the reference for the specific gravity scale)
> multiplying the S.G. obtained for the 2 gallons by 0.4 is exactly the
> correction needed for the S.G. of the 5 gallon batch.

I'd like to add a small clarification to this, just in case it's not
obvious to everybody. You have to subtract out the 1.000 from the S.G.
reading first, then multiply by 0.4 (or whatever the ratio of volumes
is), then add the 1.000 back in.

So, for example, if the measured S.G. of the 2 gallons was 1.100, you
would multiply 0.100 by 0.4 to get 0.040, yielding a corrected S.G. of
1.040.

If any of you have doubts about this, consider the case where it's all
water: the original and corrected S.G. readings should both be 1.000.

-- John Polstra jdp@polstra.UUCP
Polstra & Co., Inc. ...{uunet,sun}!practic!polstra!jdp
Seattle, WA (206) 932-6482

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