Evan and Danny, the cell runs on a 100 minute cycle (the output dial represents how many minutes the cell will be energized during that 100 min) at the end of the cycle the computer updates the main display number using, as Evan said, the average of the instant readings while the unit was energized. The unit will generate as long as the average is within the 2600 - 4000 ppm, however the high or low light may blink if the unit senses too much or too little salt. If you know the salt level is good but the unit is reading high or low, you can slave the main number to the instant by pressing the diagnostic button 5 times to get to the -XXXX instant display and switch the unit from auto to super and back to auto.
A couple of things I've seen throw the instant reading off -
Low - running a garden hose into the skimmer to refill the pool will dilute the salt reading and give a false low
High - dumping salt directly into the skimmer or sweeping a big pile into the MD - I've also put chunks of salt which wouldn't readily dissolve (the bags had gotten wet and then dried) into the skimmer to hasten the dissolution - only to see the High light flashing

HTH