A metrology method for a static interferometer, comprising: a beam splitter adapted for splitting an incident beam towards a first and a second mirror, the first mirror having N reflecting surfaces (S 1, S 2, S 3,..., S N), which are substantially planar and parallel to each other, said surfaces being offset with respect to each other and achieving N first step heights (h M1 (x)), the second mirror having M reflecting surfaces (S' 1, S' 2, S' 3,..., S' M), which are substantially planar and parallel to each other, said surfaces being offset with respect to each other and achieving M second step heights (h M2 (y)), the step heights (h M1 (x), h M2 (y)) corresponding to the distance between each surface (S 1, S 2, S 3,..., S N, S' 1, S' 2, S' 3,..., S' M) and the splitter, so that both mirrors (M1, M2) provide a plurality of reflected beams having among them optical path differences (δ(x,y)) equal to N*M horizontal checksums of the first step heights (h M1 (x)) and the second step heights (h M2 (y)), said method being characterized in that it comprises at least the steps of: - acquiring an intensity interferogram (I(x,y)) from a monochromatic incident beam, - estimating said N+M first and second step heights (h M1 (x); h M2 (y)) by solving an equation system linking the measured intensity I(x,y) to the N+M first and second step heights, said system making use of the correlations and geometric dependencies of the mirrors, and - deducing the N*M optical path differences (δ(x,y)) from the N+M first and second step heights. a beam splitter adapted for splitting an incident beam towards a first and a second mirror, the first mirror having N reflecting surfaces (S 1, S 2, S 3,..., S N), which are substantially planar and parallel to each other, said surfaces being offset with respect to each other and achieving N first step heights (h M1 (x)), the second mirror having M reflecting surfaces (S' 1, S' 2, S' 3,..., S' M), which are substantially planar and parallel to each other, said surfaces being offset with respect to each other and achieving M second step heights (h M2 (y)), the step heights (h M1 (x), h M2 (y)) corresponding to the distance between each surface (S 1, S 2, S 3,..., S N, S' 1, S' 2, S' 3,..., S' M) and the splitter, so that both mirrors (M1, M2) provide a plurality of reflected beams having among them optical path differences (δ(x,y)) equal to N*M horizontal checksums of the first step heights (h M1 (x)) and the second step heights (h M2 (y)), said method being characterized in that it comprises at least the steps of: - acquiring an intensity interferogram (I(x,y)) from a monochromatic incident beam, - estimating said N+M first and second step heights (h M1 (x); h M2 (y)) by solving an equation system linking the measured intensity I(x,y) to the N+M first and second step heights, said system making use of the correlations and geometric dependencies of the mirrors, and - deducing the N*M optical path differences (δ(x,y)) from the N+M first and second step heights. - acquiring an intensity interferogram (I(x,y)) from a monochromatic incident beam, - estimating said N+M first and second step heights (h M1 (x); h M2 (y)) by solving an equation system linking the measured intensity I(x,y) to the N+M first and second step heights, said system making use of the correlations and geometric dependencies of the mirrors, and - deducing the N*M optical path differences (δ(x,y)) from the N+M first and second step heights.