How Halo works

Halo does not sell cars, broker them, or insure them. It earns nothing from any sale it records, and it takes no fee from auction houses or dealers.

Every figure in Halo can be traced to the sales behind it. Where a number rests on only a few sales, Halo says so.

Halo records public results from auction houses and dealer listings. A research agent checks for new results each week. Every new find waits in a review queue until a person has checked it, and only then does it count.

Sales in pounds, euros or Swiss francs are held until a reviewer enters the dollar price. Unsold lots are kept as high bids and never treated as sales. Private collection data never enters a public figure.

A car's value is built from comparable sales of the same model and variant, weighted by how close each one is on date, mileage, specification and condition. The result is a range with a typical figure, and a confidence reading based on how many comparable sales there are and how close they are.

Each index follows a fixed set of models. A model's value in any month is the median of its recorded sold prices over the previous 12 months. With fewer than 3 sales in that window, its last value is held and marked as held, so one sale can't swing the index.

Indexes are equal-weighted and chain-linked: each month an index moves by the average of its models' month-on-month changes. Each is set to 100 in its first month with enough models priced. Months where fewer than half the models had fresh sales are marked as thin data and shown hatched.

Indexes are recalculated after every weekly research run.

One figure from 0 to 100 for the whole market and for each index. It averages six readings from the last 90 days:

• Sell-through: the share of auction lots that sold rather than stalling below reserve.
• Above benchmark: the share of sales above the model's value before the sale.
• Unsold high bids: where high bids landed against the model's value on cars that didn't sell.
• Volume: the number of sales against the usual level.
• Days to sell: how quickly listings sell.
• Breadth: how many models rose in value over three months.

Below 35 is cold, 35 to 50 flat, 50 to 65 firm, 65 to 80 strong, and above 80 hot. With fewer than 8 sales in the window, there is no rating.

Each model can carry an editor's rating from 0 to 100 for significance and desirability, with buying notes called The Low Down. These are opinion. They are always labeled as opinion, they are reviewed by a person before anyone sees them, and they are never used in any valuation, index or rating.

Search a chassis number or VIN to see every recorded sale and listing of that car. Only an exact number counts as a match. Sales that look like the same car but carry no number are shown as possible matches until a reviewer confirms or rejects them.