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).
English: Picture of a piece of peridotitic (green) mantle xenolith within a (dark) volcanic bomb from the Vulkan-Eifel, Germany. Coin of one euro for scale.
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share alike – If you alter, transform, or build upon this work, you must distribute the resulting work under the same license as the original.
to share – to copy, distribute and transmit the work
to remix – to adapt the work
Under the following conditions:
attribution – You must give appropriate credit, provide a link to the license, and indicate if changes were made. You may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use.
share alike – If you alter, transform, or build upon this work, you must distribute the resulting work under the same license as the original.
{{Information |Description={{en|Picture of a piece of peridotitic (green) mantle xenolith within a (dark) volcanic bomb from the Vulkan-Eifel, Germany. Coin of one euro for scale.}} {{nl|Zelf gemaakte foto van een nl:vulkanische bom uit de [[:nl:Eife