I'm probably not going to make your day, by telling you that they may both be 'right'!

For all salt test methods used by pool owners -- who don't have access to an analytical lab -- the difference between 2600 ppm and 3100 ppm is within the error range of the test methods. In other words, your likely actual salt level is probably somewhere between 2400 and 3300! If you are using test strips, than the error range on those is more like 2000 - 4000 ppm!

If you want to know your salt level more accurately, or if you want to calibrate your SWCG, the most accurate readily available kit is the Taylor K-1766. You can order it from Amata via Amazon: Taylor K-1766.

Accuracy on those kits is rated as better than 1 drop (200ppm) + 10%. This means your error around 3,000 ppm would be ± 500 ppm (300 + 200), but it would probably do better than that. It's not a bad idea to get that kit -- the sensors on SWCGs can 'drift' and recalibration assures you that your SWCG is not 'beating its head against a wall' by trying to generate chlorine when there's not enough salt in the pool.

[ Mark and I were posting at the same time. I'm surprised that the field accuracy of the Taylor unit is that good -- but they do try to be careful in their accuracy ratings. The K-1766 is the ikt he's talking about. Also, if it sounds like we're contradicting each other, we're really not, so re-read our posts. ]