A reference-standard device (20) for calibration of measurements of length, comprising a substrate (10) that includes a surface (10a) having at least one calibration pattern (11). According to the invention, this pattern comprises a plurality of nanometric structures (14), said nanometric structures (14) having one and the same section in the plane of said surface and having the same nanometric dimensions, in particular less than 50 nm, said nanometric structures (14) being arranged at a distance from one another by a constant pitch of nanometric length, in particular less than 50 nm, in at least one direction, said nanometric structures (14) being arranged within spatial regions (12) delimited in one or more directions in the plane of the substrate (10), said nanometric structures (14) being obtained via application to said substrate (10) of a process of nanostructuring (100) by means of a mask of block copolymers in order to make calibrations of measurements of length of the order of nanometres.