I did understand what you meant with calibrating with rodi/distilled water. That is in your directions for the unit.
In RHF's paper he explains how many measuring devices are off on the slope of units. The user would never know it unless the compare it to a known standard.
If you have not compared it to a known standard and think it's a good unit, it can/could be off.
He also shows how to make a standard using table salt. It's very accurate.
I just don't know if this particular unit you own is capable of calibrating with a standard of 1.026.
I may or may not be going down the wrong road with your SG being off but it is worth checking out just the same. SPS are very particular about the water SG that they live in.
