Hmm, err, that could be misleading... 4ish for visible lengths in a large class. But especially in a small group, one can use reference objects of sand (mm) and flour (fine 100 um, ultrafine 10 um). The difference between the 100 um and 10 being more behavioral and feel (eg mouth feel) than unmagnified visible size. Thus with an outdoor view (for 100 m), one can use less-abstract "it's like that there accessible length" concrete-ish analogues across like 8 orders of magnitude. Or drop to 6, or maybe push for 9, as multiples of 3 nicely detent across SI prefixes.