The 'data' value in the Cursor Location/Value tool is always showing the true data value of the image pixel, as compared to the 'Screen value', which shows the stretched monitor values between 0 and 255. When looking at Rule images, the 'rule value' depends on the type of classifier that you used. For example, if using a minimum distance classifier, the rule values represent Euclidean distance from the class mean for that training data class. For spectral angle mapper, the rule represents spectral angle (in radians) of the reference spectrum and each pixel. For more information on each classifier rule, you should refer to the ENVI Help for that particular classification algorithm.