Why are there + signs all over the pictures of the various astronauts walking on the moon?
All this time I thought it was just stage lighting shining through a tear in the backdrop.
It seems to me that if you were faking the moon landing, having these markings on the photos would not be a good idea. People could compare the positions of far off features in the background and prove that they are only tens of meters away, not many kilometers.
Such arguments, of course, never convince the truly committed.
New noun “fiducial” for me. Neat. “Something held in trust.” A number of definitions for the word as used n physics is here: memidex.com - This website is for sale! - memidex Resources and Information.
I wonder if the ANSI people use it. Who else does beside photogrammatologists? (People who take pictures of Derrida?)
The related word “fiduciary” is used by lawyers, again about trust.
Fiducial marks are used in all sorts of things that need to be scanned or placed precisely and automatically into machines.
Printers, have a look at the flaps on your cereal box, and that sort of thing.
The alternative is to throw a banana into shot for scale… (I read on imgur.)
I did some work on a research project in the late 70’s to study whether the rotation speed of the Sun had changed since the time of the earliest sun spot drawings, and we put fiducial marks on the pages of the book at top, bottom, left edge and right edge of each of dozens of daily drawings, as well as at the center of the sun’s disk. Then I measured sun spot centers using a digitizer, which at that time looked like a drafting table with a big puck. The puck was a bit like a Ouji board puck, with a window in the center that held an indicator. The periphery of the window had a coil embedded in it which communicated with wires in the table to determine position.
More recently I’ve studied motions of materials passing through machines from photographs, and used built in physical things like bolt heads and the corners of labels as fiducial marks within the images.
Bananas are also used as a standard for radiation measurements…the BDU as it it known.
AKA: Registration marks.
Those cross marks also appear on maps–such as land-survey maps; in Los Angeles County they are shown with fine red lines on pages of the Thomas Brothers street atlases to indicate corners of “sections” (single square miles, laid out and numbered) wherever they appear on the mapped area, even in the urbanized part of the county. Except for historical land grant areas like Rancho Sausal Redondo.
Unfortunately, the hoax theorists have great fun with the reticles. Some of the crosshairs appear to go behind objects. This, they claim, somehow proves the pictures are fakes.
Obviously not a Mary Poppins fan. You don’t remember the Dawes, Tomes, Mousley, Grubbs, Fidelity Fiduciary Bank?
Correct–and that underlay my “neat” and query about the word use in other fields.
Lotta things need geometrics. No printer or production editor would ever say anything but “registration” for this application of the concept.
ETA: I guess I thought it was understood that "fiducial/fiduciary " is the one usage of the word, in its more fundamental etymological sense; which is known to most everybody as something to do with money/banks.
Even in banking, it just means ‘trust’. The idea is you can ‘trust’ this bank with your money 
I just assumed that the moon was a large pilot biscuit.
A nice survey would be of “common and weird things used as informal optical measuring references.”
We had a fun thread on colloquial ones used in differing countries–“x football fields long” or “10 Empire State buildings.”
Of course hail never has its own size (e.g., 3 mm). It’s always the size of something else.
We had a hail storm the other night. The hail stones were as big as hail stones!