How does Cdi work?

https://preview.redd.it/7s4vw9w3gulg1.png?width=2560&format=png&auto=webp&s=305c115a8494168f92f020471f1dfd9d130a1c59

I spent 160 euros to play Msfs2024 and I just dont get how cdi works. The cdi bar just doesnt moves to the middle and the game always gives me rank c. Please help!