We have constructed a quasimonolithic crystal consisting of two offset, parallel-mounted quartz (101¯0) crystals for determining the wavelengths of x-ray transitions on an absolute scale without the need for reference lines. The design and organization of the quasimonolith crystal device, as well as the determination of the relevant parameters and their corresponding uncertainties are discussed. A calibration chain is established that enables linking any wavelength measurement directly to optical wavelength standards and thus to SI units. Our analysis shows that absolute wavelength measurements with an uncertainty of one part per million are in principle possible with the device. Implementation of the quartz quasimonolith in a high-resolution vacuum spectrometer used to study x-ray line emission from an electron beam ion trap is described. ©1997 American Institute of Physics.