I read that it's 1/1 by volume, not weight. Makes sense. Devcon sells their epoxy in double plunger applicators, which squeeze out equal amounts by volume, not weight.
Thorough mixing is really the key.
I mix by eye. I lay out what look like equal lines of hardener and epoxy (don't ask how I know about laying out lines), and then mix away. I use D2T mostly for anchoring hardware, not top coating, so I mix it with a wooden toothpick on a piece of duct tape laid onto my work bench, or in a small plastic salsa solo cup.
Mixing small amounts makes thorough mixing easier.
For larger amounts, I use a piece of wire with two 90 degree bends at one end, like a square U, so it gets into the edges of the solo cup.
Or a popsicle stick cut square at the end.
Whatever you mix with, mix like crazy!