Three shops quote the same bracket: $8.40, $11.10, $14.90.
The instinct is to take $8.40. The useful reaction is to measure the spread first, because that number tells you whether you ran an auction or three different conversations.
Two numbers, ten seconds
Range ratio — the crude one, and the one to start with:
spread = (max − min) / min
= (14.90 − 8.40) / 8.40
= 0.77 → 77%
Coefficient of variation — better when you have four or more quotes, because one outlier can't dominate it:
mean (μ) = (8.40 + 11.10 + 14.90) / 3 = 11.47
variance = Σ(xᵢ − μ)² / n
= ((−3.07)² + (−0.37)² + (3.43)²)/3 = 6.99
σ = √6.99 = 2.64
CV = σ / μ = 2.64 / 11.47 = 0.23 → 23%
Competent shops with similar equipment buying the same bar stock land within roughly 15–20% of each other. That band is competition. Outside it, the suppliers priced different parts.
| Spread | What it usually means | What to do |
|---|---|---|
| < 20% | A real market | Award on lead time and past performance |
| 20–50% | One supplier read the spec differently | One clarifying email to the outlier |
| > 50% | The RFQ was ambiguous | Re-issue with the missing detail |
At 77% and CV 23%, our bracket is in the third row.
Finding which line caused it
The range tells you that something is wrong. Line items tell you what. Normalise each supplier's lines to the cheapest quote for that line:
| Line | Shop A | Shop B | Shop C | Max/min |
|---|---|---|---|---|
| Material | $3.10 | $3.25 | $3.40 | 1.10 |
| Machining | $4.05 | $4.40 | $4.60 | 1.14 |
| Setup (per pc @ 500) | $1.25 | $1.20 | $1.30 | 1.04 |
| Finishing | — | $2.25 | $5.60 | ∞ |
Material and machining agree within 14%. The entire spread is one line: finishing. Shop A quoted no finish at all, Shop C quoted a finish three times richer than Shop B. Nobody was wrong — the drawing didn't say.
That's the whole diagnostic: the line with the highest max/min ratio is the line your RFQ under-specified. You now know exactly which sentence to add before re-issuing.
Why the cheap quote is the risky one
The low quote is the one most likely to have missed something, because missing something is how it got low. Shop A at $8.40 hasn't offered you a discount; it has offered you an unfinished part. That cost reappears as a change order, a first-article rejection, or a slipped delivery — at which point you are paying twice and have lost the date as well.
How this gets solved
None of the above works if three PDFs get rekeyed into one spreadsheet column called "cost". The arithmetic needs the line items to survive the journey.
RFQTrace has suppliers quote against your itemised list rather than returning a lump sum, so every quote arrives with the same rows in the same order. The comparison view then puts them side by side, which makes the max/min-per-line table above something you read rather than something you build.
The feature isn't finding a cheaper supplier. It's showing you, before you award, that your cheapest number was answering a question you never asked.