A technique has been developed for constructing a unified fundamental equation of state of an individual substance for a wide range of state parameters. The technique is based on the Benedek hypothesis and the method of pseudocritical points, which are based on the assertion that the isochoric and isobaric heat capacities, the isothermal compressibility coefficient, and the speed of sound in the vicinity of the critical point on the critical and noncritical isochores are described by power-law dependences with the same critical indices. A unified fundamental equation of state of argon has been created that satisfies the requirements of the theory of scaling of critical phenomena, transforms into a virial equation of state in the gas region, satisfactorily conveys experimental data on density, isochoric and isobaric heat capacities, and sound speed within the uncertainty of the initial experimental data in the single-phase region in a wide range temperatures and pressures, on the phase equilibrium line in the range from the triple point to the critical point and in the near-critical region. On the basis of a unified fundamental equation of state, tables of standard reference data for argon were developed and certified in the temperature range of 83.806– 1200 K and pressures of 0.1–1000 MPa, and a statistical estimate of the accuracy of the tables was made.
