It is required to use any iPad Air (2013, IOS 12.4) or later models with screen size equal or higher than 9.7" (iPad mini not recommended). We have designed our apps considering the variability of screen brightness properties of several iPad generations in such a way you can use it in any iPad without a previous calibration. Anyway, if you desire to increase the reliability of your measurements, specially on Contrast Sensitivity, please read carefully this section.