What does "fiducial" mean?

Fiducial: Having the nature of a trust; fiduciary; as, fiducial power. Spelman. Fiducial edge (Astron. & Surv.), the straight edge of the alidade or ruler along which a straight line is to be drawn. -- Fiducial line or point (Math. & Physics.), a line or point of reference, as for setting a graduated circle or scale used for measurments.