How DeaLynx computes what it shows

The measurement chain in four steps

1. 1. Daily reading

   The displayed price and availability of each product are read every day directly on the retailer page (or through Amazon data for Amazon products). Only new items are tracked: used and refurbished are ignored. Every reading is timestamped and kept.

2. 2. Cleaning

   A reading that deviates by more than 40% from its neighbours (third-party seller, extraction error, recycled reference) is discarded. A price “holds” until the next reading, but never more than 14 days without confirmation, so an old isolated reading does not weigh for months.

3. 3. Usual price

   Median of the prices recorded over the last 180 days, weighted by how long each price stayed displayed. At least three distinct prices are required. It is the reference for every discount shown on DeaLynx.

4. 4. Score and verdict

   The 0 to 100 score compares today’s price with the usual price, with a bonus when it approaches the observed floor (10th percentile) and a penalty when it exceeds the ceiling (90th percentile). It is pulled towards 50 when the history is short. Verdict: excellent deal from 80, good deal from 60 to 79, average price from 40 to 59, bad time below.

Glossary

Usual price

Weighted median of the prices actually recorded over six months (180 days), outliers removed. It is what the product ordinarily costs, regardless of strike-through prices.

Strike-through price

Reference price displayed by the retailer next to the selling price, often the launch or recommended price. DeaLynx records it but never uses it as the basis of a discount.

Fake discount

Product showing a strike-through price while today’s price stays at 98% or more of its usual price: the advertised discount saves nothing compared with the ordinary price.

Real discount

Today’s price at least 5% below the usual price. Monthly reports use a stricter 15% threshold for a “real drop”.

Deal score

A 0 to 100 rating that judges today’s price against the usual price, floor and ceiling observed over six months, weighted by the reliability of the history.

Verdict

Reading of the score: excellent deal (80 and above), good deal (60 to 79), average price (40 to 59), bad time (below 40).

Floor and ceiling

Weighted 10th and 90th percentiles of prices over six months: the range in which the price usually moves, excluding exceptional peaks and dips.

Reading

Timestamped reading of a product’s price and availability at a retailer. A reading identical to the previous one extends its validity instead of creating a duplicate.

Availability

The product can be bought from the retailer at reading time (active buy button, pre-orders included). “Coming soon” or “unavailable” count as not purchasable.

Buy Box (Amazon)

The offer Amazon features on a product page. DeaLynx keeps the Buy Box price only when it is new; a used or Warehouse Buy Box is not a price.

Fake discount barometer

Weekly measurement, over the whole purchasable catalogue, of the share of products below their usual price and the share of strike-through prices that save nothing. Archived month by month.

Outlier reading

A price deviating by more than 40% from its three neighbours in time. Excluded from the usual price, floor and ceiling.

Known limits

A recently tracked product has a short history: its score is deliberately pulled towards 50 while confidence is low. Recorded prices are those displayed at reading time, excluding shipping and promo codes. For retailers with local stock (stores), only the price trend is tracked.

These definitions may be quoted freely with the credit “DeaLynx methodology” and a link to this page.