Addition

I may be being really stupid here, but in the mark book I am trying to make it total 4 marks out of ten in a fifth column out of 40. Any advice welcome!

Welcome bentait,
Here a couple of images that hope will help.
In this particular case, when you are not 'averaging', the Grade Type must be set to - generic grade (numeric) - , for all columns.

This is the configuration


And here the result


If you still can't solve it let me know in which step you're in , and I'll provide further instructions!
Regards,

That's perfect - thank you!