Hello @Matty,
You’re Welcome. 
I’m glad I was able to help you.
And I forgot to mention it during my previous response that there was no need for apologies. I’m glad you asked your queries for better understanding of the concept. Always happy to help because we also learn some new things when members ask questions on the forum. Ask your queries freely without any hesitation.
And lastly before I sign off I’m providing a link below of an article from Alberto Ferrari. I recommend you to go through this article once where he has explained about although “DAX is simple, but not easy.”
Hoping you find this useful.
Thanks & Warm Regards,
Harsh