Alkmaar's Cheese Market at the Waagplein (square by medieval weighing house) is 400 years-old, one of 4 Dutch Cheese Markets, opening every Friday morning between April and September. The scene is demonstration how such merchants' markets were operating in post-medieval days. Traditionally Dutch farmers were bringing their cheeses to town's main square to sell. Teams of official guild cheese-porters (kaasdragers), identified by different color hats showing the belonging to various companies, carried cheese on barriers, which typically weighted about 160 kg. Buyers then sampled the cheese and negotiated a price using a ritual system (handjeklap) in which buyers and sellers clap each other's hands and shout prices. Once the price were agreed, carriers brought cheeses to weighing house and company's scale. In such markets only were sold only locally made cheeses.