I hit my 1/3 sugar break on Thursday night, and was too busy Friday to even look at my fermenter. Today, I measured 24.5 bx which is almost halfway for my mead. Corrected that is about 1.084 SG. Started at 1.135, expect to hit 1.024. So, that's 0.111 points to max out the ABV for this yeast. Half of that is .55. The calc is then 1.135 -0.55 = 1.080 for halfway point.
That means my mead is already over 7% ABV, so a gentle stir daily (or so) helps keep the yeast in suspension and working towards their goal.
D47 has never given me sulfur problems, so good to hear your yeasties are happy!
As for the refractometer readings, they should be consistent. Logically, the fermenting must is at the same throughout. So, it may be your cleaning process in between samples, leaving some moisture on the lense, or uneven coverage (bubbles) when laying the light-cover on the sample.
My process begins after taking a reading.
+ rinse refractomter lense & light plate with water
+ pat dry with paper towel.
+ set on shelf with light plate open to allow lens & plate to dry completely
+ the next day, it is all dry and ready for 3-4 drops on the lens, push the light plate over and tap gently to get out bubbles
Hope that is helpful in some way!
--LexusChris