Patek Philippe produced 349 examples of the reference 2499 from 1951 to 1985. The model was made in four series, the majority in yellow gold.
The first series featured square chronograph buttons, Arabic numerals and tachometer scale. The second with round chronograph buttons, either baton or Arabic numerals and tachometer scale (see the next lot). The third, also with round buttons but simple dial with baton numerals.
The actual owner purchased the present watch from Patek Philippe Geneva on 27 August 1983. It is from the fourth series, made from around 1978 until 1985, which resembles the third but with a sapphire crystal. In 1986 the model was replaced by reference 3970 (see lot 186 in this sale).
A similar watch is illustrated in Patek Philippe Wristwatches by Martin Huber & Alan Banbery, 2nd edition, p. 302.