Metrology Of The The Coaltrade At Liege In The 19Th Century: When they try to calculate the production of the collieries of Liège, historians use the cartload, and at that a uniform cartload of 1.800 kilos. Actually, in the first half of the past century two different kinds of carts (the "tombereau de Liège" and the "voiture de Meuse") were used. Neither of them had a uniform capacity, even if in 1844 it was decided that the former should be equal to 16 hectoliters, the latter equal to 24 hectoliters. Another difficulty was that, whereas the capacity of the carts was expressed in hectoliters, the actual production of coal was expressed by its weight. From 1845 on, all official records express the quantities in weight and no longer in terms of capacity. The conversion rule is 1 hectoliter equal to 90 kilos. Before 1823, on the other hand, there is no such general rule at all. For that reason, one should be very careful when trying to use the figures of coal production as given in the documents.