On 16 September at 15:38:52.188 UTC we asked nine public price ser­vices the same ques­tion at the same moment: what does one bitcoin cost? Every request left our server within a few mil­lisec­onds of the others. All nine answered. No two gave the same number.

The answers ran from $75,666.93 to $75,742.70, a range of $75.77, about 10 basis points on a single asset, asked a single ques­tion, in the same second. It was a dif­fer­ent second from the one the rest of the issue is built on: price ser­vices cannot be asked about the past, so we asked them about a present of our own, and every page that shows these answers is stamped with that other second.

None of them is wrong. Each answered a slightly dif­fer­ent ques­tion and says which one in its doc­u­men­ta­tion. The dis­per­sion is the visible dif­fer­ence between def­i­ni­tions.

Nine ques­tions that sound like one

Three ser­vices, Kraken, Bitstamp and Gemini, returned the last trade on their own books: the price at which some­body most recently bought or sold there, however small the trade and however long ago. Coinbase returned its own spot price for its dollar market. OKX, Deribit and Bybit returned indices, each built from a basket of other exchanges by their own rules, the kind of number page 19 took apart. CoinGecko returned an aggre­gate across a very large number of venues.

Binance returned some­thing else again: the average trade price over the pre­vi­ous five minutes, in tether. It answered a ques­tion about the recent past, not the present, in a dif­fer­ent unit. Bybit's index was also in tether. The two highest answers in our sample were the two denom­i­nated in tether, which is exactly what page 12 would predict.

The ages

Some ser­vices stamp their answers with the time the number was made. Most of those stamps were a frac­tion of a second old. CoinGecko's was 112 seconds old when it reached us. It was not broken; it refreshes on a sched­ule, and between refreshes the last number stands, pre­cisely like a quote on a quiet venue. Three ser­vices gave no time­stamp at all, so we cannot say how old their numbers were. We can only say when we received them.

Which one was right?

Each, for its purpose. A trader on Kraken needs Kraken's book. A futures exchange decid­ing whether to liq­ui­date some­body needs an index no single venue can push. An accoun­tant needs a doc­u­mented source at a doc­u­mented time. The mistake is the belief that there was a tenth number under­neath the nine that was simply the price. If machines looking at the most liquid object of its kind dis­agree by tens of dollars, nobody should be sur­prised when people pricing a paint­ing, a house or a used car dis­agree by far more.

We asked nine times and got nine answers. We report all nine, with their def­i­ni­tions, their ages and their units, and we do not average them.