LOL...just when i think i got it!!! Never considered the dilution...DAMN!!
Back to the drawing board...
Hahahaha! This hobby... and this site... will give your brain a workout, that's for sure.
I am currently fermenting a 'test' sack mead.
Since we are dealing with volume and mass, I filled the gallon jug to the very top with water and poured out an amount equal to what I want to add for honey (shooting for 4.5 lbs, but won't be upset if i dont get all the way there). I do this, for instance, by pouring from the full jug into empty 3 pound honey bottles. THAT I did without even a scale. This was the easy part. Filled one of the 3 lb bottles to match a full bottle of honey (right to the neck), then divide that so that 2 bottles have an equal amount (the area that 1.5 lbs of honey takes up) in each bottle, then I fill one of them all the way up. This makes enough room in the jug for 4.5 lbs of honey.
EUREKA! EUREAK!
Then I added three pounds of honey to start. This has the added virtue of keeping the level low enough to avoid an eruption.
When the density drops to 1.010, I will add 5 oz of honey, which should raise it to 1.020. When it drops to 1.010 again, I will add another 5 oz of honey, etc, etc, etc, until the yeast will no longer ferment honey due to the alcohol percentage. The last addition of honey (whether its the 3rd or 4th or 5th) will leave some residual honey, and I'll let it sit, stabilize it and then decide whether or not to add a touch more for sweetness.
This avoids the dilution problem.
I HAVE over-made batches to have something to top off with, and I've now got a freezer full of half-full water bottles of different musts. I am thinking of one day adding them all together and seeing what happens.
CG: Maybe I'll clean and polish some pebbles, put one carefully in each bottle, and bill the brew as "Stone Mead". <very big grin>
See ya,
Joe