The magnetic and electronic properties of ultrathin Co films have been found to depend sensitively on their growth and structure. Therefore, the authors studied the evolution of Co films during their deposition onto Cu(100) substrates under UHV conditions by STM. Their STM-design offers a simple way to retrieve particular positions on a sample even after preparations like sputtering or annealing, which require multiple sample transfers to a preparation stage. They have observed the nucleation and growth of individual Co islands during the growth of films from the sub-monolayer regime up to several monolayers. At room temperature, the system exhibits epitaxial growth in a nearly ideal layer-by-layer mode. The density of island nucleation is significantly higher in the growth of the first monolayer, compared with additional layers. The onset of growth of the second layer is well before the completion of the first layer, contrasting the more perfect growth of subsequent layers.