 Frontal presentation is now regarded as preferable when deriving equal-loudness contours, and the latest ISO standard is specifically based on frontal and central presentation.The Robinson-Dadson determination used loudspeakers, and for a long time the difference from the Fletcher-Munson curves was explained partly on the basis that the latter used headphones.However, the ISO report actually lists the latter as using "compensated" headphones, though it doesn't make clear how Robinson-Dadson achieved "compensation".