I have a sketch with 3 entities. a line, a tangent arc and
another tangent line. I want the total length of all 3 entities to
be 8.80".

"D2@Sketch2"+"D3@Sketch2"+"D1@Sketch2"=8.8

Why doesn't this equation work?

"D2@Sketch2"+"D3@Sketch2"+"D1@Sketch2"=8.8

Why doesn't this equation work?