Its caliber is an August Agassiz 4 (AA4). On November 6, 2018, Longines announced discovery of serial number 183, dated October 23, 1867, currently the Oldest Longines watch known. Longines Serial Number 183 'Attesa' date 1867 In his analysis, David concluded the Swiss watchmaking industry needed to change significantly to keep pace with its American competitors. Upon returning, David wrote a 108-page report detailing what he learned during his trip the report is considered one of the most significant documents in watchmaking history, detailing the inner workings of American watch factories, including the entire production process, from raw materials to finished watches, and the highly-effective internal structure and quality control measures implemented in American factories. Francillon sent Jacques David to the 1876 World’s Fair in Philadelphia to gather new ideas and strategies from American watchmakers. watchmaking industry was earning making strides in industrialized watch manufacturing.

The innovative movement won an award at the 1867 Universal Exhibition in Paris. The 20A, built with an anchor escapement (usually employed in pendulum clocks), was wound and set via a pendent crown. By 1867, it was also marked the year the Longines factory produced its first in-house watch movement, the 20A. In addition, Francillon appointed David as Technical Director and put him in charge of the new factory. To help further his efforts to improve the production at Longines, Francillon brought on Jacques David, a talented engineer. Imier known locally as Les Longines (“long meadows”), gave rise to the Longines name. Francillon solidified his firm’s progression to mass production in 1867 by establishing his first factory.

Under Francillon, the company began segueing out of the établissage system and moved towards more modern production methods.

Later, when Agassiz started suffering from ill health, he passed leadership to Francillon. One early stroke of genius from Francillon was to solely produce crown-wound pocket watches rather than the prevalent key-wound alternative. Francillon was the mastermind behind several impressive innovations that would distinguish the company from its competitors. Several years later, Agassiz brought in his bright, enterprising nephew, trained economist Ernest Francillon, into the business. By 1846, Raigeul and Morel had retired from the watch industry, leaving Agassiz as sole company head. Auguste had two partners, lawyers Henri Raiguel and Florian Morel the company's original name was Raiguel Jeune & Cie. Longines was founded in Saint-Imier in 1832 by Auguste Agassiz, a Swiss watchmaker and brother of biologist Louis Agassiz.

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