Weighing, not measuring
Updated
Volume has no place in this craft. Wax is measured by weight, fragrance by weight, dye by weight.
Everything by weight
A vessel's stated capacity is a volume and the wax that fills it is a weight, and the two are joined by the wax's density.
So "an 8 oz jar" does not take 8 oz of wax. It takes roughly 80 percent of that by weight, and the exact figure is something you establish by filling one and weighing it.
Percentages of what
Fragrance load is a percentage of the finished candle, oil included, not a percentage of the wax.
At 10 percent, 1,000 g of finished candle is 900 g of wax and 100 g of oil. Treating it as 10 percent of the wax gives 1,000 g plus 100 g, which is 9.1 percent, and the difference is enough to change a tested candle.
Pick a convention, write it on the formula sheet, and use the same one every time.
The scale
One reading to 1 g for wax, which is plenty at these weights.
One reading to 0.1 g or better for fragrance and dye. Dye in particular is dosed at fractions of a percent.
Tare properly, check against a known weight occasionally, and keep the scale off a surface that gets knocked by a heavy pot.
Recording it
Write the actual weights, not the targets. A batch that came out right at 9.4 percent when you aimed at 10 is worth reproducing at 9.4.
And record the lot of the wax and the oil. When a batch burns differently the first question is which lot, and that is only answerable if it was written down at the time.