gravimetric factor
Suppose you weigh a basket of fruit-and-net together but really want to know how much fruit alone you have. If you know what fraction of each weighing is fruit, one multiplication gives you the answer. The gravimetric factor plays exactly that role in weighing chemistry.
The gravimetric factor is the ratio that converts the mass of the weighed solid into the mass of the analyte you actually care about. It is built from molar masses: the mass of analyte per formula unit divided by the mass of the weighed compound, adjusted for how many analyte atoms each formula contains.
It matters because the thing you weigh is rarely the thing you report. You might weigh barium sulfate but need to report sulfur, or weigh iron(III) oxide but report iron. The factor is the clean bookkeeping that turns one mass into the other.
To report iron from weighed Fe2O3, the gravimetric factor is (2 × 55.85) ÷ 159.69 ≈ 0.6994; multiply the oxide's mass by this number to get the mass of iron.
Multiply the weighed mass by the factor to get the analyte mass.
Always check the atom-counting. If the weighed formula contains two analyte atoms but you report one atom at a time, the factor must include that 2 — a missed coefficient here silently halves or doubles the result.