This post was first thought to be only an answer to a
question, but I think that it can be used for other purposes as well and gave it it's own post.
The shape provides a field in which you can write freely formulas referencing other shapes, without the need of opening the shapesheet.
the syntax is relatively simple to understand:
1) [shapeName] references ShapeName!prop.value
2) if you want to access a different prop, you need to write it in the shapesheet syntax ie: ShapeName!prop.RowName
It comes with 3 sub-shapes containing the name, the value and the formula.
The formula can be hidden by dragging its control under the value sub-shape.
As the controls can glue to the controls of other shapes, you can easily make calculation blocks, that show or hide the formulas.