china graphs are great, they are a bit like crayon, so you can wipe clean for the following year, but they will stay put even in the dishwasher, (they are made for marking china in the food industry) you "sharpen" them like a charcoal pencil so they last for years, most art suppliers should be able to get them for you. the marks stay put and you can reuse your markers, brilliant

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Yo an' Bob
Walk lightly on the earth
take only what you need
give all you can
and your produce will be bountifull