A method can include performing a single-read operation at a read reference voltage to detect bits from memory cells. Dummy data is previously programmed into the memory cells. Original bits of the memory cells can be determined based on a default read reference voltage and known values of the dummy data. The detected bits and the original bits are compared to determine an upper-state failed bit count (FBC) corresponding to the memory cells having threshold voltages shifted from above the read reference voltage to below the read reference voltage and a lower-state FBC corresponding to the memory cells having threshold voltages shifted from below the read reference voltage to above the read reference voltage. When a difference between the upper-state FBC and the lower-state FBC being smaller than a threshold, the read reference voltage can be determined to be a best read reference voltage.