The Hayward units display both a running average salinity level as well as an "instant" salt reading. You may need to reset the running average. However, if the salt test is showing 2800ppm and the cell is reporting 2700ppm, that's actually well within the margin of error for the unit. You should really never "recalibrate" the unit as that can lead to lots of problems and, in any event, the Hayward cells have the most accurate and reliable readout of salt so there's really no reason to recalibrate it.
What salt test are you using? Strips are only good to +/-400ppm (and that's being generous) while the K-1766 kit reads chloride levels at +/-200ppm BUT can be made more accurate by simply testing a volume of water larger than the standard 10mL sample (a 40mL water sample gives 50ppm/drop of titrant). I always recommend the K-1766 as it is the most accurate and reliable measure of chloride concentration and has almost no interferences.
Assuming all of your numbers are correct, 2800ppm is typically the lowest possible operating point for most SWGs. Most SWG manufacturers spec a normal operating salt level at 3500ppm. So, if your reading is correct, you really want the salt level a little higher, perhaps somewhere between 3000-3200ppm.
Also note that salt can take a long time to both dissolve AND mix into pool water. Salt water, especially saturated salt water in and around where the salt granules are added, is very dense and can take a long time to mix and homogenize. Salt should be added to the water and then brushed around until it dissolves. After it is visibly dissolved, it is best to vigorously brush the pool and run the pumps for 24 hours to ensure the salt is adequately mixed. The SWG should not be turned on until proper mixing is achieved.
