Why is important to include a measuring instrument (such as a ruler) in close-up photos?

A photographer will often include a ruler in the shot to establish scale but always takes a duplicate image without the measuring device. In court, the defense could claim the device covered something important. And of course, pictures are of no value unless they're in context.

i think its white blood cells

i hope this

acceleration = 18/3 = 6 m/s per second.

hope i

-lavira: )