If by real value of the course you mean in 0-100 scale, you can set the grade display type of the course total to percentage. But then again it depends on how your {4,5,6,7} should be interpreted in 0-100 scale. If it is not simple 25% for each value you will probably need to use a formula to do the calc of the course total.
Gradebook
Change min&max grade value
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