How to cut watermelon
Depending on the size, cut the watermelon into quarters or eights with a very sharp, large knife.
Now sit a tranche on a chopping board, rind side down, and look at it: the seed layer runs in a crescent halfway down the tranche. With your sharp knife, slice the flesh off just above it. Reserve it to make juice or a granita dessert from it.
Use a large fork to scrape the seeds out, it’s really easy albeit messy. You can trim the flesh after scraping if you want very neat cubes. Then make incisions into the flesh down to the white rind, every 2cm or thereabouts.
Now make a sweeping cut along the base, leaving the white rind behind, to release the chunks, and cut them into cubes.
They can be stored in a bowl in the fridge for up to 5 days.