in reply to
Re: The best object to provide scale on a photo showing a small object is:
in thread The best object to provide scale on a photo showing a small object is:
A ruler would be shown in such a way that you see the markings, so the actual length of the ruler is irrelevant. There's still the problem that the markings could be in centimiters or inches. You can usually decide which it is from the number of subdivisions, but not always. Cds are good for the same reason: even though there are cds of smaller size than the normal, the hole is always the same.