Hi Steve … You almost got the steps correct. You have to Subtract the Wet weight from the Dry weight which gives you a third number. Then you divide the Dry weight by the third number (Difference) to get the SG. ;)) So in formula it is: Dry - Wet = x then Dry/x = SG.
Of course there are correction factors for the temperature of the Water, but generally at room temperature or below (but above 32 F) the measurement is close enough. ;)) The reason for the temperature corrections is that Water gets denser as it approaches 32 F.
Technically, water reaches its maximum density at 4 C, then decreases slightly until it freezes. Doesn’t have much effect on sg measurements, tho.
If you’ve never purchased a stone, have never had someone purchase a stone for you and have never traveled
to Tanzania, then you don’t have Tanzanite, because the ONLY mine is located in Tanzania. I would say you have colored glass.