Geneva 15.7%. Of the agricultural land, 0.3% is used for growing crops. Of the water in the municipality, 0.2% is composed of lakes and 2.9% is rivers and streams. The altitude of Geneva is , and corresponds to the altitude of the largest of the Pierres du Niton, two large rocks emerging from the lake which date from the last ice age. This rock was chosen by General Guillaume Henri Dufour as the reference point for surveying in Switzerland. The second main river of Geneva is the Arve, which flows into the Rhône just west of the city centre. Mont Blanc
Geneva such as Caterpillar, DuPont, and Cargill have their international headquarters in the city; Take Two Interactive, Electronic Arts, INVISTA, Procter & Gamble and Oracle Corporation have their European headquarters in the city. Hewlett Packard has its Europe, Africa, and Middle East headquarters in Meyrin, near Geneva, as does PrivatAir. There is a long tradition of watchmaking in the city, which dates back to the 16th century. Many watchmakers have been based in Geneva since their foundation, such as (Baume et Mercier, Charriol, Chopard, Franck Muller, Patek Philippe, Rolex, Universal Genève, Raymond Weil, Vacheron Constantin and Frédérique Constant). Two major international