You can display a 10 cm ruler
Graphics[{Line[{{0, 0}, {10, 0}}],
Table[Line[{{x, 0}, {x, -1}}], {x, 0, 10}],
Table[Line[{{x, 0}, {x, -.5}}], {x, 0, 10, .1}], Thick,
Table[Line[{{x, 0}, {x, -1}}], {x, 0, 10}],
Table[Line[{{x, 0}, {x, -.7}}], {x, .5, 9.5}],
Table[Text[Style[n, 24], {n, -1.5}], {n, 0, 10}]}]
and then draw any graphic to a relative scale.
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