Sorry, been very busy yesterday, out of office.
When I said “we”, I meant me and you and all other from Ignition community.
We all have access to forum and docs which are full of examples.
As I see you already figured out the expression tag.
For scripting you have to decide where and when the script will run.
In this case I would use the tag change event for L9 and L10
Create a new memory tag, long named ReverseVal
On both L9 and L10 go to EditTag->Tag Event Scripts, click edit ->Value Changed
Now you can add the following code :
lowInt = system.tag.read("[default]L9")
highInt = system.tag.read("[default]L10")
ReverseVal = 65535 * highInt.value + lowInt.value + highInt.value
system.tag.write("[default]ReverseVal", ReverseVal)
If you have different path just change it. From your image I cannot see full path.
Example is taken from Inductive University , Tag Event Script lesson.
Feel free to add protection as script to fire only when you need it to.
Now it will fire at any change, no matter quality, connection and so on.