My office has a metal-framed awning window (i.e. a casement hinged at the top). To stop it closing under its own weight, it has an arm either side, the other end of which slides along a vertical track. (This also limits how far the window can be opened.)
The other vertical side (not visible in the photo) is symmetric with the visible one. Note also the solution I improvised to stop the handle of the blind banging in windy weather. :-)
The problem is, the track is not that stiff, so while it keeps the window open in usual circumstances, a gust of wind will blow the window closed. There's no mechanism to tighten the tension of the track or lock it in position.
I've tried wedging a small object between the outer and inner frames, but sometimes a gust will relieve the tension of the object, making it fall out of position. I've also tried bending a paperclip into a U shape, which I can fit into the track as an end stop, but the paperclip isn't springy enough (or maybe it doesn't have enough friction), so it doesn't lock in position.
How can I keep the window slightly open without having to keep reopening it? All the usual office supplies are available, and I also have access to electronics tools and supplies such as pliers, cables, solder.