The Archaeological Institute of America, San Diego Society has been
designated as a source for the printing and distribution of centimeter
scales  used by the National Park Service, archaeologists, museums,
universities, geologists, photographers and many others around the
world.

The set of two scales, used to indicate object size in photographs,
comes with one each, 19 x 3 cm. and 12 x 2 cm. The scales are only
$6/set including first class postage, and US $7/set for foreign orders.
Better stock up now... Authorized purchase orders accepted.
For information or ordering just click on
http://www.theglyph.com/scales.html

These may be an item that should be offered in museum gift shops...what
do you think?

Or order from:
AIA San Diego Society
2014 Siegle Drive
Lemon Grove, CA 91945