A three-way match tolerance is the deviation permitted between the purchase order, the goods receipt and the invoice below which an invoice is approved without human review. It exists because insisting on exact equality would send almost every invoice to manual handling, and three-way matching would stop being an automation.
Tolerances are set on two dimensions and in two forms. The price dimension covers unit price and line total; the quantity dimension covers units received against units ordered and billed. Each can be expressed as an absolute amount, which suits rounding and small freight differences, or as a percentage, which scales with line value. Most configurations combine both and apply whichever is lower.
Both failure modes are damaging, and they fail in opposite directions. A tolerance set too narrow routes everything to review; the queue grows, the team approves in bulk to clear it, and the control becomes theatre while consuming real hours. A tolerance set too wide lets every small overcharge through, and because each invoice passes cleanly, nothing is ever flagged. The leakage is invisible precisely because the control reports success.
The second case has a consequence rarely stated: a tolerance behaves like a published threshold. A supplier whose invoices sit consistently at 1.5 percent above contract price where the tolerance is 2 percent is not making rounding errors. Systematic one-sided variance inside the band is a pattern, not noise, and no per-invoice check will ever surface it.
Setting the threshold well therefore starts from the observed distribution of variances rather than a round number chosen at implementation. Phacet analyses variance across invoices rather than one at a time, which is what turns supplier price variance into overbilling prevention instead of a per-line pass or fail.
