Dimension the slot width and make the Radius Typical. Dimension the overal slot length from the tangent point on the arcs. You can add true position callout if you so desire with boundary conditions or edge profile....that would depend on your machine shop. Check ASME Y14.5M for reference on this.
Best Regards,
Heckler
"Never underestimate the power of very stupid people in large groups" John Kenneth Galbraith