Groat Supply is a slate which has a mass of 0 and is worth 0.
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slate contains the following message:
Some of my groats have yet again gone missing. I am working to rectify the situation, but unfortunately you will have to make due with two groats instead of the promised five.
I am sure that a man that has been in business as long as you have knows how to stretch supply, but this is still unacceptable. As soon as I figure out what is happening to my groats, your next delivery will be free.
Malik