can you draw an elliptical arc? Pretty much just a section of an ellipse

Not directly.  You can draw an ellipse, and then hide a part by drawing something else over it.

Nice idea. With a bit of maths, you might be able to use dc.setClip() and then dc.drawEllipse() to do that.

Not sure a clip region would do much here, as that limits you to a rectangle Being able to use a polygon to obscure a part might be handy.

I'd probably just stick with an arc and not bother with an ellipse.

I've thought about it but setClip is a fairly new feature (v2.3) and I'd like my watchface to be able to run on my own watch, which runs v1.3

I have made a watchface that has a round arc going around the edge to indicate the seconds. So far it only supports round and semi-round watches and I'd like for it to also support rectangular ones, which is why I thought of the eclipse.

Jim, to explain the clip region;

1. An ellipse segment is simply part of an ellipse. 

2. Setting clip to have top as y-r2, bottom as centre y of ellipse, left as x-r1 and w to match ellipse r1*2 gives a perfect half ellipse. 

3. Adjusting sideways (keeping y the same) can give any segment between a perfect half and a segment up to pi radians or 180 degrees. 

4. Same logic applies to vertical. 

You can’t get some arcs 3/4 ellipse, for example, but you can draw a large range of arcs. 

Or you could... but the OP says they cannot use setClip as targeting older CIQ, so...

A useful theoretical one for another project. 

You're missing that you can do the same thing with a rectangle and there's no need for a clip region.

Clip regions are needed for 1hz, but most times, not needed.  (so older devices can be supported)

Draw the full ellipse, and using other things like a circle/rectangle/line/polygon. overlay what you want hidden with the background color.  Some depends on where you want the arc to begin and end.

Agreed that it’s just an alternative route to the same end, but are you saying there’s a disadvantage to setClip and clearClip?

They seem almost purpose built to do in a single line what would otherwise take several. 

Eg:

With clip to draw an elliptic arc from 1.1*pi to 1.9*pi:

setClip, drawEllipse, clearClip

With rect instead:

drawEllipse, fillRect (lhs), fillRect (rhs), fillRect (base).

Plus, with clip, I can do it in any order where with rect, I need to draw the arc first and overlay. 

So is there an additional cost to clip?

The power of clip regions is really 1hz WFs.  You need to use them to stay under the 30ms power budget.  While they can be used for other things, as is seen here, aren't compatible with all devices.

Using an example of something like an ellipse where you want to show the normal 5 segment move bar, you'll still have to overlay parts.