For more than a century and a quarter ships' crews of the world's voluntary observing fleet have made meteorological and surface current observations. Those observations recorded in the ships' logbooks are the backbone of the Marine Archive now held in the Meteorological Office, Bracknell, UK. Much use is made of computer processing for providing suitable statistical data which form the basis of maps and current roses. This article outlines the method of processing used in the Netherlands, illustrating various situations the observer at sea may encounter. The supposition that the use of modern navigation equipment could hamper the making of current observations is discussed, and situations that could cause the reduction of accuracy and reliability of current mean values are mentioned. In essence: how reliable are surface current observations from ships collected in the past few years, and particularly those that will be collected in the years to come?