The Cezanne has gone to Stavros Niarchos, one of the world's richest and most discerning art collectors, but leading London dealers in scientific instruments are still mystified by the calculator battle.
The gilt and lacquered brass, mechanical calculator by J C Schuster was estimated by Christie's at pounds 15,000- pounds 20,000 but a Swiss clock dealer, Edgar Mannheimer, bought it for pounds 7.7m over the telephone; his competitor was an unidentified German. Mr Mannheimer is said to have been acting for a German private collector.
'It is a real mystery,' Harriet Wynter, a Kensington dealer, said. 'It is a very fine instrument but it only dates from the beginning of the 19th century. It has no historical significance.'
Sebastian Whitestone, of Bobinet, said another 20 or so similar calculators are known to exist.
There were other unexpected highs in a month characterised by erratic auction results. Man Ray's Glass Tears became the world's most expensive photograph when it fetched pounds 122,500 at Sotheby's, multiplying the pounds 20,000- pounds 30,000 estimate roughly five times. But 31 per cent of the photographs were left unsold.
The superb Rodchenko photographs at Christie's the day before had made lacklustre prices with eight out of 24 unsold.
It is a narrow market and the connoisseurs are choosy.
The same goes for Rembrandt prints, to judge by Sotheby's sale of etchings collected over the last 60 years by the German connoisseur Otto Schafer. A wonderful example of Rembrandt's portrait of his friend Jan Six doubled estimates to reach dollars 618,500, but there were no takers for two impressions of The Three Crosses, a much rarer print.
A fourth state impression of The Three Crosses made dollars 990,000 three years ago, so Sotheby's thought they were playing safe with an estimate of dollars 200,000-dollars 300,000 for Schafer's fourth state - the prints Rembrandt made from his plate as he changed ideas and reworked it have been classified as different 'states'. Schafer also had a second state impression of The Three Crosses which was estimated at dollars 600,000-dollars 900,000 but neither sold.
Several American collectors of Old Master paintings turned out to bid on the Rembrandt etchings which saved the sale - 61 out of 72 prints found buyers. But Old Master paintings are not themselves a sure fire market; 40 per cent of the paintings in Sotheby's New York sale were left unsold and 38 per cent at Christie's.
The best price of the month was the Fr9m pounds 1.1m paid in Paris for a portrait by Jean-Etienne Liotard; it was painted in Constantinople around 1740 and depicts an English businessman and the daughter of the French consul, both in Turkish dress.
The worst result of the month was Sotheby's Old Master sale in Madrid on 18 May where 65 per cent of the paintings went unsold. The Prado Museum took advantage of the occasion to aquire two paintings and four drawings at prices ranging from pounds 2,130 to pounds 95,600.
The US is currently the strongest collectors' market. This was born out by the new record price for a 19th century American painting at Sotheby's, the dollars 5.5m ( pounds 3.5m) for an impressionist style interior, The Room of Flowers by Childe Hassam (1859-1935) and by the sale of a first printing of the Declaration of Independence for around dollars 2m.