Vertical distance indication

Hi, I have been trying to implement a code where I can show an arrow (or maybe a raycast) indicating the vertical distance between two objects. Any help will be appreciated.

Thanks.

This is how I got it to work:

I follow the example this YouTube video (https://www.youtube.com/watch?v=km_kU-j7mcw) and I it is close to what I want so I stick with it