I would challenge the need to track partial completion. A well-crafted item in a checklist is either done or it is not.

If your concern is about indicating that you started something and are now waiting on results, then I would argue that there are actually 2 separate items there ("do the thing" and "receive the results").

The problem with a "partial completion" indicator is that it doesn't really tell you anything about how much of the thing is still left to do. You'll have to think about it when you come back to it, which you will do anyway if you simply leave the item unchecked.