Indeed
Double Zero the only point of the marks were so that the person analyzing the film on the x/y plotter could bring the cross hairs of the cursor back to roughly the same place on the weapon/aircraft in successive frames so as to get a reasonably accurate velocity etc. In my days when computers filled whole rooms and ran on valves, most of the results were hand plotted on graph paper and the errors smoothed out by eye. The edges of the aircraft tended not to be always well defined all the way through the film, twas exceeding annoying to get half way through a job and find the datum point had gone. Even worse when the only equipment was a projector and a piece of paper to plot with.
I used to use the more precise marks for ground trials where the lighting could be better controlled, the image to frame size larger (usually) and perhaps a 1000fps film speed to ensure the image remained reasonably sharp, or as you said for on board high speed cameras.
Sorry guys wallowing in nostalgia at the moment, I'd better shut up I think.
