The easiest way to get uniform cubes is to first cut a whole melon in half. Place the melon half cut side down on a cutting board. Using a very sharp knife, cut the melon into slices about 3/4 inch thick. Next, holding the melon together, turn it 90 degrees and slice it crosswise. Now you'll have watermelon "sticks" which are very easy to cut into cubes. Discard or compost the rind or save it for pickling