I am probably mistaken, but it seems to me that so many asking about sg don't seem to understand that it is different for every glaze and how each potter likes the way it looks on his or her clay. One potter may like a certain glaze a bit on the thick side for his clay and another might like the way the same glaze looks quite thin on her clay. They will find a sg that works for them
There is no hard and fast rule for what each glaze should be--I have changed the sg on some of my glazes when I have changed the clays I use...please correct me if I am wrong or if I have not expressed this right. Also remember to keep your liquid measurements very accurate...sometimes just a few grams can make a difference.