There are many cases when absolute measurements of objects with large height differences or height
discontinuity is needed. These measurements can not be covered by classical interferometry since the range of non-ambiguity
is limited to half the optical wavelength. Several techniques have been already developed for extending of
non-ambiguity range. However most of them is based on multi-wavelength methods which demands expensive light
sources and special environment conditions. In this work the new interferometric technique for absolute measurements of
large steps discontinuities is proposed. Variable wavefront of the illuminating beam and special procedure for calibration
of the measurement volume are used for extending of the measurement range without using multispectral sources.
Additionally, calibration of the measurement area simplifies fringe processing and quicken measures. Theoretical
analysis of this technique, its numerical simulations and experimental verification are presented and discussed.