Over limited temperature ranges many simple molten salts follow an Arrhenius law, and on a log-viscosity versus 1000/T plot that law is a straight line whose slope is the activation energy. Dial the measurement uncertainty from the few percent careful campaigns achieve to the wider spread historically seen between laboratories, and watch how much freedom the same data leave in the fitted slope. The axis rescales so the band and the steepest admissible fit always stay inside the frame.
Schematic Arrhenius line with illustrative parameters; the slope-freedom estimate is a geometric bound over the plotted window rather than a regression confidence interval. Published reference correlations should be consulted for real values.