Gravity Readings

Both as specific gravity, from a hydrometer or a refractometer. If your FG came from a refractometer, correct it for alcohol first — raw readings run high once fermentation begins.

Apparent attenuation is what most brewing software reports, and it overstates how much sugar actually converted — alcohol is less dense than water, so it drags the final gravity reading down further than the remaining sugar alone would. Real attenuation corrects for that, giving a more accurate picture of how thoroughly your yeast actually finished the job.