A method for operating a memory that includes a plurality of analog memory cells includes storing data in a first group of the memory cells by writing respective first cell values to the memory cells in the first group. After storing the data, respective second cell values are read from the memory cells in the first group, and differences are found between the respective first and second cell values for each of one or more of the memory cells in the first group. The differences are processed to produce error information, and the error information is stored in a second group of the memory cells.