Construction of isotherms around the liquid- and supercritical-to-ice VII transition for temperatures between 300 K and 1000 K. Isotherms within this range cross from region 4 to region 7 through an interpolation region from 5.8 · 10⁸ Pa to 2 · 10⁹ Pa, except the 301.99 K case which goes up to P_4-to-3 (the boundary marking the transition from region 4 to ice VI in region 2). Across the interpolation region, a cubic spline (shown in red) was used to connect the original AQUA isotherm (solid lines) to the new data from Mazevet et al. (2021) (dashed lines) with the +425 J/(kg K) shift applied. After the spline, the Mazevet et al. (2021) data is followed by the isotherms at 457.98, 851.14 until the boundary between region 7 and region 3 is met, which occurs at 3.53 · 10⁹ Pa, 2.23 · 10¹⁰ Pa. After this boundary, the original AQUA is followed again until 3 · 10¹¹ Pa, after which the isotherms are linearly extrapolated (brown lines). The grey curves show the final, revised isotherms.