Remove tomato tops and wash with basil

Place glass jar on the scale and zero

Add tomatoes and basil to the jar (196g including roughly 10 basil leaves and the remaining weight tomatoes)

Fill the jar with water and note the final weight (389g)

The sum of the equation is the salt you need to add, stir this salt into the decanted water and then pour the mixture back in to the tomatoes and basil

Fill a plastic bag with a little water to act as a weight