Fiducial /(?)/

Fi·du·cial

Fiducial

a.
  1. Having faith or trust; confident; undoubting; firm.
  2. Having the nature of a trust; fiduciary; as, fiducial power.

Phrases & Compounds
Fiducial edge
the straight edge of the alidade or ruler along which a straight line is to be drawn.
Fiducial line
a line or point of reference, as for setting a graduated circle or scale used for measurments.