In the 1920s, experimental techniques could not distinguish between the results κ = 0 (assumed by Millikan and Laurtisen) and κ = 2 (predicted by the original Fowler–Nordheim-type equation). However, it should now be possible to make reasonably accurate measurements of dlni/d(1/V) (if necessary by using lock-in amplifier /phase-sensitive detection techniques and computer-controlled equipment), and to derive κ from the slope of an appropriate data plot.