Afraid this is another new starter question that demonstrates how little I know....

In the attached part there is an round ended slot sketched but not yet done as a cut into the body. I don't know how to sort the last relationship that finishes its correct alignment.

The slot needs to be aligned vertically so that the centre point of the slot is aligned with the centre of the raised boss on the left, This all happens to be on the horizontal centre line of the complete object.

I am sure I could do the sums that work out the actual distances and then dimension some part but to my old 2D thinking thats the hard way and not a relationship as such,

to explain a little further this items is something i drew years ago in 2D autocad and I am redrawing it in SolidWorks for the practice and to be able to show it and other parts yet to be drawn as an assembly. The original was drawn by stick down a horizontal and vertical centre line and then many of the other lines were done as offets from these. Thats an approach that doesnt seem to work in Solidworks and I have ended up measureing dimensions on the autocad drawing to get an actual value where what i really wanted was "in the middle" or "equidistant"

Grateful for any help with this particular question or my general approach. I am still drawing to learn but have made it over the hurdle of hating something new to wanting to know more and messing with this when i really ought to be doing something else

Paul