  The volume of tantalum versus pressure has been accurately measured up to 101
GPa by single-crystal x-ray diffraction, with helium as pressure transmitting
medium. Slight deviation from previous static determinations is observed.
Discrepancy with reduced shock-wave and ultrasonic data supports recent doubts
about the calibration of the ruby pressure scale. Finally, first principle
calculations of the literature show a positive curvature in $P(V)$ relative to
the experimental data, even with a modified pressure scale.
