However, the Input filed where I have done the expression, when I view the page doesnt appear. I have redone the expression with just the first 2 fields being added together and ensured they are visible (reusable elements without value are not visible) but still it does not appear.

For instance I need to add together all the percentages from each entry to ensure it is 100%. Or the total cost, so add each amount each entry is worth (they vary).

What do you mean the data isnt available. There is values in each field

you should have the list of data entries somewhere in the reusable element, likely a repeating group. Then you can in a dynamic expression reference the repeating group list of things, then select the data field that is the percentage and then use the sum operator.

Repeating groups list of things each items percentage sum

Thanks so much for that. Once I understood what you meant It made sense. A hell of a lot easier. I have so much to learn and I have to change my way of looking at things. I keep looking at the page and seeing that this is what Im working with but there is another layer underneath that you can work with and it can be so much easier. I really appreciate your help