fiducial, fi-dū′shi-al, adj. showing confidence or reliance: of the nature of a trust.
As regards the fiducial lines, they might be drawn on the glass screen; but black lines are not, I find, the best.
It gives, in short, the average tint of every unit of area in the picture, measured from the fiducial lines as co-ordinates.
The cistern should not, however, require adjustment to a zero or fiducial point.
It is upon this focusing-screen in the roof that I see the fiducial lines by which I make all the adjustments.
These lines are our fiducial lines, and all colours can be referred to them.