This product has attributes and a minimum qty and units.
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Mixed is OFF this means you CANNOT mix attributes to make the minimums and units.
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The Size Option Value: Select from Below ... is a Display Only Attribute. 
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This means that the product cannot be added to the Shopping Cart if that Option Value is selected. If it is still selected, then an error is triggered when the Add to Cart is pressed with a warning to the customer on what the error is.
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No checkout is allowed when errors exist.