Using coins for scale is discouraged as it will require people unfamiliar with them to look up the dimensions or guess, both of which defeat the purpose of the object in the first place. Coins can also reinforce a geographical bias, and some coins' designs are copyrighted.
Ideally, a photograph should include a ruler with the subject (example) or an added scale marking.
SI ("metric") units are the most commonly used worldwide (see meter and centimeter).
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Captions
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Common rifle cartridges, from the largest .50 BMG to the smallest .22 LR
Items portrayed in this file
depicts
M2 Browning
.50 BMG
Barrett M82
copyright status
copyrighted, dedicated to the public domain by copyright holder
copyrighted
copyright license
released into the public domain by the copyright holder
inception
25 February 2006
media type
image/jpeg
File history
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{{Information |Description=Rifle cartridges - L to R: .50 BMG, 300 Win Mag, .308 Winchester, 7.62 Russian Short, 5.56 NATO, .22 LR |Source=http://en.wikipedia.org/wiki/Image:Rifle_cartridge_comparison.jpg |Date=25 February 2006 |Author= Richard C. Wysong