A method for obtaining the shape and thickness variation of an object with parallel surfaces such as a wafer comprising: initiating an unequal path interferometer assembly having two unequal path interferometers, comprising: a first reference flat in the first interferometer; a second reference flat in the second interferometer; a cavity defined by a distance between the first reference flat and the second reference flat; a wafer holder (172, 174) to receive the object in the cavity such that an optical path remains open around the object at an outer annular area between the first reference flat and the second reference flat, wherein the wafer holder comprises first and second wafer holding devices (172, 174); and at least one wafer holder motor (170, 176) coupled to the wafer holder (172, 174) such that the object may be tilted in the cavity as to allow for measurements of local areas of interest, wherein the first and second wafer holding devices (172, 174) are tilted together simultaneously by the at least one wafer holder motor (170, 176); receiving an object into the cavity; receiving a coherent tunable light source to the unequal path interferometers assembly; recording multiple optical interferograms in response to known phase shifts produced by changes in the wavelength of light from the tunable source; extracting phases of each of the interferograms to produce multiple phase maps; determining each map from its corresponding interferogram; determining from each map local areas of interest with high slopes; tilting the wafer holder to allow measurement of the high slope areas of interest; and processing measurement that covers the entire surface of an object including the high slope areas of interest. initiating an unequal path interferometer assembly having two unequal path interferometers, comprising: a first reference flat in the first interferometer; a second reference flat in the second interferometer; a cavity defined by a distance between the first reference flat and the second reference flat; a wafer holder (172, 174) to receive the object in the cavity such that an optical path remains open around the object at an outer annular area between the first reference flat and the second reference flat, wherein the wafer holder comprises first and second wafer holding devices (172, 174); and at least one wafer holder motor (170, 176) coupled to the wafer holder (172, 174) such that the object may be tilted in the cavity as to allow for measurements of local areas of interest, wherein the first and second wafer holding devices (172, 174) are tilted together simultaneously by the at least one wafer holder motor (170, 176); a first reference flat in the first interferometer; a second reference flat in the second interferometer; a cavity defined by a distance between the first reference flat and the second reference flat; a wafer holder (172, 174) to receive the object in the cavity such that an optical path remains open around the object at an outer annular area between the first reference flat and the second reference flat, wherein the wafer holder comprises first and second wafer holding devices (172, 174); and at least one wafer holder motor (170, 176) coupled to the wafer holder (172, 174) such that the object may be tilted in the cavity as to allow for measurements of local areas of interest, wherein the first and second wafer holding devices (172, 174) are tilted together simultaneously by the at least one wafer holder motor (170, 176); receiving an object into the cavity; receiving a coherent tunable light source to the unequal path interferometers assembly; recording multiple optical interferograms in response to known phase shifts produced by changes in the wavelength of light from the tunable source; extracting phases of each of the interferograms to produce multiple phase maps; determining each map from its corresponding interferogram; determining from each map local areas of interest with high slopes; tilting the wafer holder to allow measurement of the high slope areas of interest; and processing measurement that covers the entire surface of an object including the high slope areas of interest.