Expression for a gauge in VC

Hi,

I'm new to VC. Trying to create a gauge on a query. In my iview, I have a query which displays data in a table (Force Element and Material Readiness).

I added a form view connecting it with the table. In the form, i added a gauge "NUM1". now I'm trying to enter an expression for this field but have no idea how to do this.

Please help.