Depends on your purposes, I suppose.
I said on some other thread… I’d dispute there’s such a thing as a 3m chart. It’s just a chart with some letters of different sizes. You can look at it from any distance you like. Just have to be aware of how to interpret the results. A “3m chart” should have letters exactly half the height of a “6m chart” so it’s trivial to convert between the two. (eg if you stand 6m from your 3m chart). Other distances or other chart “sizes” are slightly less trivial.
- Also valid to pick a line and track how close you have to stand in order to be able to read it.
If you are looking for something to active-focus on, just stand at a distance where there’s some blur, and clear it up.
Wearing normalised, 3m is probably too close to stand, since blur horizon would be of the order of 4m anyway. But could wear differentials and stand a bit closer.